DOE's Office of Science

WASHINGTON, DC - DOE's Office of Science today announced that 61 scientists from across the nation will receive up to $15.3 million in funding for research as part of DOE's Early Career Research Program. The effort, now in its fourth year, is designed to bolster the nation's scientific workforce by providing support to exceptional researchers during the crucial early career years, when many scientists do their most formative work.

"By providing support to the most creative and productive researchers in their early career years, this program is helping to build and sustain America's science workforce," said Patricia M. Dehmer, Acting Director of DOE's Office of Science. "We congratulate this year's winners on having competed successfully for these very selective awards, and we look forward to following their accomplishments over the next five years."

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KICP Members: Clarence L. Chang
Scientific projects: South Pole Telescope (SPT)

by Steve Koppes, The University of Chicago News Office

Scientists heard their first pops last week in an experiment that searches for signs of dark matter in the form of tiny bubbles.

They will need to analyze them further in order to discern whether dark matter caused any of the COUPP-60 experiment's first bubbles at the SNOLAB underground science laboratory in Ontario, Canada. Dark matter accounts for nearly 90 percent of all matter in the universe, yet it is invisible to telescopes.

"Our goal is to make the most sensitive detector to see signals of particles that we don't understand," said Hugh Lippincott, a postdoctoral scientist with Fermi National Accelerator Laboratory. Lippincott has spent much of the past several months leading the installation of the one-of-a-kind detector at SNOLAB, 1.5 miles underground.

COUPP, or the Chicagoland Observatory for Underground Particle Physics, is a dark-matter experiment funded by the Department of Energy's Office of Science. Fermilab managed the assembly and installation of the experiment's detector. Leading the experiment is Juan Collar of the Kavli Institute for Cosmological Physics at the University of Chicago.

"Operation of COUPP-60 at SNOLAB is the culmination of a decade of work at the University of Chicago and Fermilab," said Collar, an associate professor in physics. "This device has the potential to become the most sensitive dark matter detector in the world, for both modes of interaction expected from Weakly Interacting Massive Particles."

The COUPP-60 detector is a jar filled with 60 kilograms of purified water and CF3I - an ingredient found in fire extinguishers. The liquid in the detector is kept at a temperature and pressure slightly above the boiling point, but it requires an extra bit of energy to actually form a bubble. When a passing particle enters the detector and disturbs an atom in the clear liquid, it provides that energy.

Dark matter particles, which scientists think rarely interact with other matter, should form individual bubbles in the COUPP-60 tank.

"The events are so rare, we're looking for a couple of events per year," Lippincott said.

Other, more common and interactive particles such as neutrons are more likely to leave a trail of multiple bubbles as they pass through.

Over the next few months, scientists will analyze the bubbles that form in their detector to test how well COUPP-60 is working and to determine whether they see signs of dark matter. One of the advantages of the detector is that it can be filled with a different liquid, if scientists decide they would like to alter their techniques.

"We are already working on a 500-kilogram chamber, to be installed in the same site starting in 2015," Collar said.

The COUPP-60 detector is the latest addition to a suite of dark-matter experiments running at SNOLAB. Scientists run dark matter experiments underground to shield them from a distracting background of other particles that constantly shower Earth from space. Dark matter particles can move through the mile and a half of rock under which the laboratory is buried, whereas most other particles cannot.

Scientists further shield the COUPP-60 detector from neutrons and other particles by submersing it in 7,000 gallons of water.

Scientists first proposed the existence of dark matter in the 1930s, when they discovered that visible matter could not account for the rotational velocities of galaxies. Other evidence, such as gravitational lensing that distorts the view of faraway stars and the inability to explain how other galaxies hold together if not for the mass of dark matter, have improved scientists' case. Astrophysicists think dark matter accounts for about a quarter of the matter and energy in the universe. But no one has conclusively observed dark matter particles.

The COUPP experiment includes scientists, technicians and students from UChicago, Indiana University South Bend, Northwestern University, University of Valencia, Virginia Tech, Fermilab, Pacific Northwest National Laboratory and SNOLAB.

- This article was adapted from a Fermilab announcement:
http://www.fnal.gov/pub/presspass/press_releases/2013/Dark-Matter-Detector-2013.html

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KICP Members: Juan I. Collar
Scientific projects: Chicagoland Observatory for Underground Particle Physics (COUPP)

The University of Chicago News Office

Pioneering University of Chicago cosmologist Michael S. Turner focuses his remarks on "the Chicago School of Cosmology," from Edwin Hubble and George Ellery Hale to the present. Hubble, SB 1910, PhD 1917, discovered that the universe consists of billions of galaxies and that it has been expanding since it began in a big bang. Hale was the first chairman of the University's Department of Astronomy and Astrophysics. He also founded Yerkes Observatory, which under his leadership developed the big reflecting telescopes that are the workhorses of optical astronomy today, making discoveries from the expanding universe to planets orbiting other stars. Turning to more recent times, Turner discusses efforts that started in the 1980s at UChicago to establish the new field of particle astrophysics and cosmology. At that time, the Chicago School, consisting primarily of the late David Schramm, Edward "Rocky" Kolb, the Arthur Holly Compton Distinguished Service Professor in Astronomy and Astrophysics, and Turner, was alone in pushing this idea. "Today this idea that there are deep connections between the very big and the very small is universally accepted, has propelled the field to its current prominence, and underpins our understanding of the universe," Turner said. "As we say at Chicago, ideas matter!" The Ryerson Lecture grew out of a 1972 bequest to the University by Nora and Edward L. Ryerson, a former chairman of the board of trustees. The lecture honors excellence in academic pursuits. A faculty committee selects the Ryerson Lecturer based on research contributions of lasting significance.

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The University of Chicago News Office

Nobel laureate James Cronin, SM'53, PhD'55, will receive the Alumni Medal, the highest honor for a UChicago alumnus, while 13 others will be recognized for their career accomplishments during Alumni Weekend.

Cronin shared the Nobel Prize in physics in 1980 for showing that the laws of nature operate differently on matter and antimatter - a discovery that opened an entirely new research direction for particle physics. More recently, Cronin led the effort to build the Pierre Auger Observatory in Argentina. The Auger collaboration has become the most successful cosmic ray observatory and has inspired more than 400 scientists in 17 countries to explore this frontier of knowledge. A professor emeritus in Astronomy and Astrophysics, Physics, and the College, Cronin is also a dedicated professor, winning the Quantrell Award for Undergraduate Teaching in 1994.

The Alumni Medal recognizes achievement of an exceptional nature in any field, vocational or voluntary, covering an entire career. In addition to the Alumni Medal, the University will recognize distinguished alumni and faculty members who have made exceptional contributions to UChicago, to their professions, and to their communities, across six different categories.

This year's 14 Alumni Award recipients include a global economist governing the Banco de Mexico, one of the developers of video game franchise Halo, a renowned statistician in both the sports and political fronts, and a philanthropist working to create a tuberculosis-free world.

The University of Chicago Alumni Association and the Alumni Board of Governors will hold the 72nd annual Alumni Awards Ceremony at 11 a.m. on Saturday, June 8 in Rockefeller Memorial Chapel. The ceremony is free and open to the public.

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KICP Members: James W. Cronin
Scientific projects: Pierre Auger Observatory (AUGER)

by Steve Koppes, The University of Chicago News Office

Prof. Edward "Rocky" Kolb has been appointed dean of the Division of the Physical Sciences for a five-year term, President Robert J. Zimmer and Provost Thomas F. Rosenbaum announced. Kolb's appointment will take effect July 1.

Kolb is the Arthur Holly Compton Distinguished Service Professor of Astronomy & Astrophysics and the College and former Chair of Astronomy & Astrophysics. He is a member of the Enrico Fermi Institute and the Kavli Institute for Cosmological Physics. In 1983, Kolb was a founding leader of the Theoretical Astrophysics Group and in 2004 the founding Director of the Particle Astrophysics Center at Fermi National Accelerator Laboratory. He presently serves on the boards of the Giant Magellan Telescope and the Adler Planetarium.

"In filling this position, we sought an outstanding scholar and leader to work with the faculty of the Division to fulfill its intellectual and educational aspirations, as well as to become a significant contributor to defining the academic directions of the University as a whole," wrote Zimmer and Rosenbaum in a joint e-mail to the division faculty. An elected advisory committee of division faculty members recommended Kolb for the post.

"For over a century, the faculty, staff, and students of the Physical Sciences Division have led just about every major advance in the physical sciences," Kolb said. "As dean, I plan to enlarge and support the activities of the Division and keep us at the leading edge."

Kolb succeeds Robert A. Fefferman, the Max Mason Distinguished Service Professor of Mathematics, who is returning full time to the faculty. Zimmer and Rosenbaum praised Fefferman for leading the Division with dedication and accomplishment over the last decade.

"Bob systematically improved every department in the Physical Sciences Division over the last decade through strategic faculty hiring, an emphasis on pedagogical excellence, and attention to intellectual culture," they wrote. "He has been a major proponent of scientific outreach and diversity, leading both through the creation of innovative programs and personal example."

A native of New Orleans, Kolb earned his bachelor's degree from the University of New Orleans in 1973 and his doctorate in physics from the University of Texas, Austin, in 1978.

Kolb's research applies fundamental particle physics and general relativity theory to the very early universe, including cosmic inflation models, gravitational production of particles, particle dark matter, ultra-high energy cosmic rays, and high-energy neutrino astronomy. In addition to more than 200 peer-reviewed papers, he co-authored The Early Universe, the standard textbook on particle physics and cosmology. In 2010, the American Astronomical Society and the American Institute for Physics recognized his research, along with his colleague Michael Turner's work, with the 2010 Dannie Heineman Prize for Astrophysics.

Kolb is a Fellow of the American Academy of Arts and Sciences and a Fellow of the American Physical Society. He was the recipient of the 2003 Oersted Medal of the American Association of Physics Teachers for notable contributions to the teaching of physics, a 1993 Quantrell Prize for undergraduate teaching excellence at the University, and the 2009 Excellence in Teaching Award from the University's Graham School of Continuing Liberal and Professional Studies.

In great demand as an international scientific and public lecturer, Kolb has been a Harlow Shapley Visiting Lecturer with the American Astronomical Society since 1984. His book for the general public, Blind Watchers of the Sky, received the 1996 Emme Award of the American Aeronautical Society. In the autumn of 2012 he was in residence at the University of Heidelberg as the recipient of the J. Hans D. Jensen Prize.

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The Kavli Foundation

Three leading scientists discuss how the world's most powerful radio telescope revealed that the most vigorous bursts of star birth in the cosmos took place much earlier than previously thought.

IN THE EARLY UNIVERSE, new stars were bursting to life at rates far higher than we see today. The Milky Way today may fire up one new star every year; but billions of years ago, a subset of galaxies in the relatively young universe were producing new stars at a rate of 1,000 per year.

Now, a multi-national team of astronomers has found that these distant, dusty galaxies were churning out stars much earlier than once believed - as early as one billion years after the Big Bang, nearly 13 billion years ago. Their study was published online on March 13 by the journal Nature. (Press releases: California Institute of Technology, ESO, KICP/University of Chicago, University of Arizona)

Measuring just how far away these galaxies are, and examining the rapid star formation going on inside them, was no trivial feat. Armed with a catalog of galaxies discovered by the South Pole Telescope (SPT), the astronomers used some fortuitous natural phenomena and the great resolving power of the Atacama Large Millimeter/submillimeter Array, or ALMA - an array of radio antennas situated on a high plateau in the Atacama Desert of Northern Chile - to learn about some of the most distant star-forming galaxies.

Three members of the team spoke recently with The Kavli Foundation in a roundtable discussion about their discovery and what they plan next. The participants:
* John E. Carlstrom - Subrahmanyan Chandrasekhar Distinguished Service Professor in the Departments of Astronomy and Astrophysics as well as Physics at the University of Chicago, and Deputy Director of the UChicago's Kavli Institute for Cosmological Physics (KICP). Prof. Carlstrom is an observational cosmologist who studies the Cosmic Microwave Background (CMB). He is also leader of the 10-meter South Pole Telescope project, which recently completed a survey of 2,500 square degrees of the sky, and is now conducting a survey of the polarization of the CMB.
* Dan P. Marrone - Assistant Professor in the Department of Astronomy at the University of Arizona. Prof. Marrone is interested in galaxy clusters, galaxy formation in the early universe, and the physics of the supermassive black hole in our galaxy, Sagittarius A*.
* Joaquin D. Vieira - Postdoctoral Scholar at the California Institute of Technology and a member of Caltech's Observational Cosmology Group. Dr. Vieira is interested in studying galaxy evolution at very high redshifts, the first stars and galaxies, and the evolution of large-scale structures in the universe. He is the leader of the group studying the galaxies discovered by the South Pole Telescope.

The following is an edited transcript with remarks added by the participants.

---

THE KAVLI FOUNDATION: About a third of the galaxies that you observed in your study existed at extremely early times, when the universe was only about one billion years old. You must all have mental picture of what the early universe could have been like. How did your findings change your views about what was actually going on then?

JOAQUIN VIEIRA: My expectations before this study were more focused on what I thought we'd be able to detect, rather than what I thought the universe was like back then. We knew we'd be excited to find anything at a redshift greater than four.

To understand what that redshift measurement means, it's important to understand, by the time it reaches us, the wavelength of light from very distant galaxies is stretched by the expansion of the universe. The result is that the light spectrum of these galaxies - that is, the rainbow of colors that make up the overall light emitted by each galaxy - has been shifted toward the redder end of the electromagnetic spectrum, from the part that's visible to our eyes toward longer wavelengths of light that make up the infrared part.

By measuring how much the light from these galaxies has been shifted toward the infrared, we can calculate how far away they are and how far back in time they existed. That's where the word "redshift" comes from, and higher numbers in the redshift scale correspond to farther distances from Earth, and farther back in time.

Now, a redshift of 4 corresponds to a time more than 12 billion years ago, when the universe was about 1.6 billion years old. That light has been traveling for 12 billion light years and when we observe those galaxies, we aren't seeing them as they are, but as they were. Observing very distant galaxies is a way for us to observe the Universe in its infancy - to look back in time.

TKF: But ALMA has changed all that.

VIEIRA: It's changed everything. After making our observations with ALMA, we doubled the number of these dusty starburst galaxies above a redshift of four. When we first started planning the redshift survey with ALMA, we had already tried with four other observatories to measure redshifts for the SPT sources - and it was very difficult and very frustrating. We basically had no success at all. We were thinking that if we got just a handful of redshifts with ALMA, we would be really lucky. But in the end we got redshifts for 90-percent of the sources in our survey catalog - out to higher redshifts then we really thought was possible.

JOHN CARLSTROM: We did expect to see bright galaxies in the South Pole Telescope survey, but not the dusty star-forming galaxies that we found. Instead, we thought we'd detect the very bright centers of galaxies where jets of radiation are emitted from black holes. These phenomena, often referred to as radio sources, are pretty well known.

Before our observations with ALMA, Joaquin had catalogued galaxies detected by the South Pole Telescope. When he analyzed the spectra of these objects, he discovered that some of the sources appeared to be dominated by emission from dust. They were not in line with what you would expect from the well known population of radio sources. This was the first clue we were onto something interesting. Then Joaquin discovered there were no counterparts to these galaxies catalogued by infrared surveys of the sky. That was baffling. It meant that they had escaped detection in the infrared surveys. No one had predicted that we would see such a luminous population of dusty galaxies so far back.

DAN MARRONE: I agree with Joaquin and John that our ability to get redshifts for these galaxies was a surprise - and that's a testament to the power of ALMA. Previously, we had tried making observations at the same wavelengths with the southernmost observatory available, the Submillimeter Array in Hawaii, and we pointed the radio dishes basically at the horizon to watch these galaxies just barely come up over the dirt. We were able to see them, but we had no real hope of getting redshifts for them. We still couldn't really figure out how far away they were. We needed something like ALMA to pull that off.

TKF: John, I wanted to come back to something that you said earlier. You said it was a surprise for you to find these dusty star-forming galaxies at such early times. When we talk about "dusty, star-forming galaxies" do we mean galaxies that show elements other than hydrogen and helium? Like iron, carbon, silicon, etc.?

CARLSTROM: By "dusty" I do mean that. When stars form, they quickly enrich the gas surrounding them with heavier elements. And those elements then form dust particles, and the dust particles absorb the starlight and then re-radiate that as a thermal emission at much longer wavelengths. We refer to that thermal radiation at longer wavelengths as "dusty emission" because it's coming from the dust. But it is actually energy that is generated by the stars that form.

TKF: These early dusty galaxies were churning out stars, as your study says, at a rate of 1,000 stars per year - compared to about one star per year for the Milky Way and other galaxies in modern times. Why do we think that star formation was so much more vigorous in the early universe?

MARRONE: In the early universe, in general, a much larger fraction of the mass of galaxies was in gas. That alone pushes up the star formation rate.

The universe also was much smaller back then, so galaxies were much closer together. As a result, we expect that they were much more likely to have interacted with one another. And collisions between two galaxies will trigger bursts of star formation. Today, because of the expansion of the universe, galaxies are further apart on average and these interactions are much less common.

TKF: In your study, you note that these early galaxies you observed are shining with the energy of a trillion suns but have masses that are much less than that. This suggests that stars burned brighter back then. Was this finding a surprise, and what does it tell us about the character of stars at these early times?

VIEIRA: When stars form, they come in a wide range of masses, from much less than the Sun to tens of times more massive than the Sun. The most massive stars are incredibly bright, but they live very short lives before they become supernovae. The energy output we measure from these galaxies shows us that the most massive stars created in the starburst have not yet used up their fuel and exploded, though they will do so relatively soon.

TKF: The team took advantage of two natural phenomena to observe these galaxies in detail: one was that their light was magnified by the gravity of closer objects - a phenomenon known as gravitational lensing. But there was a second phenomenon that’s a bit harder to understand, and it has to do with the fact that dusty galaxies are not dimmer the farther away they are. Why is this the case?

MARRONE: At wavelengths near 1 millimeter, the spectrum of dust is very interesting. It gets brighter very quickly as you look at shorter and shorter wavelengths. For example, the SPT observes these galaxies at 2 millimeters (and 1.4 and 3). If you look at a dusty galaxy at 2 millimeters and 1 millimeter wavelengths, it will be about 10 times brighter at 1 millimeter than at it is at 2 millimeters wavelength. That's for looking at the same galaxy (at the same redshift). Now imagine you look at two different galaxies at two different redshifts, but at the same wavelength. The light from the higher redshift (more distant) galaxy will have been stretched more, so you measure the light at, say, 2 millimeters wavelength, but the original wavelength will have been not 1 millimeter, but maybe 0.5 millimeters. It was 100 times brighter when it was emitted. Of course, because it's further away it looks fainter, just like a light bulb would look fainter across the street instead of in your house. But starting out so much brighter almost perfectly cancels that effect.

This is incredibly valuable for us. You have all these dusty galaxies existing throughout the history of the universe, and no matter how far away they are they're not really getting much dimmer when we look at these wavelengths. So, unlike at optical wavelengths, where distant galaxies get dimmer and dimmer and the deep sky ends up looking black, light from these dusty galaxies creates a mostly diffuse and flat infrared sky. And we call that the Cosmic Infrared Background.

TKF: And that's where ALMA comes in. It's used to measure the spectra of these dusty galaxies and determine how far away they actually are.

MARRONE: That's right. Because these dusty galaxies do not get any dimmer as they get farther away, we actually don't know where they are. But ALMA's sensitivity in measuring the spectra of each of these objects allows us to measure how much those spectra are shifted toward the redder end of the spectrum - and obtain precise redshifts.

TKF: Tell me about ALMA. How would you describe it?

CARLSTROM: ALMA is like a very high-powered telescope. Imagine you're looking through a large telescope; you need a finder scope on the side to see where you're pointing. That's because the field of view of the big telescope is so tiny. ALMA, like the big telescope, gives you this incredibly detailed image of whatever you're looking at, plus this beautiful spectroscopic capability. But it only looks a very tiny field of view.

TKF: So ALMA allows you to look much closer at galaxies already identified by the South Pole Telescope, which is being used to survey a large fraction of the sky, correct?

CARLSTROM: Yes. ALMA is most powerful when it's teamed up with other observatories that conduct surveys of huge swaths of the sky to identify interesting targets worthy of more detailed examination. It enables a detailed examination of extremely distant objects because it operates as an interferometer. That means its effective resolving power isn't equal to that of one antenna, but to an antenna that is the diameter of the entire array. So ALMA's 12-meter antennas, collectively, get orders of magnitude higher angular resolution than what you would get from the single 10-meter South Pole Telescope. As a result, ALMA gives us very, very detailed images.

TKF: So ALMA's role here was critical.

CARLSTOM: ALMA is designed to detect the exact same wavelengths of light in which the dusty galaxies were discovered by the South Pole Telescope. As a result, there was no doubt ALMA was seeing the same galaxies. Also, ALMA gives us very high spectral resolution, so we were able to analyze the light from these galaxies with great precision to identify carbon monoxide and other molecules. That told us about what’s in those galaxies, but more importantly for our study, that level of detail allowed us to measure the shifting of that spectra toward the red part of the spectrum - the redshift. And measuring changes in this part of the spectrum is the way we could tell how far away these objects are.

TKF: The ALMA observatory isn't completed. Right now it has an array of about 16 antennas, but within a year or so it will have 66. How will this help you in the future?

MARRONE: With little more than a dozen antennas at ALMA, we were able to make very detailed images of these galaxies - and that was after just 2 minutes of observations per galaxy. When we were trying this with The Submillimeter Array in Hawaii - which has only eight antennas, each only half the size as the ones at ALMA - we were observing each galaxy for a couple of hours. Even then, we were not getting anything like the detail that ALMA gave us, though this is a little unfair to the SMA, since it had to look so low on the horizon to see our sources. When ALMA is completed, the observations we obtained for this first study are just going to be trivial. You almost feel bad using ALMA to look at them - the exposures are so fast. You want to give ALMA more of a challenge.

CARLSTROM: I would add that a key science goal for the James Webb Space Telescope is to study the very first galaxies that emerged in the universe. This telescope is regarded as the successor to the Hubble Space Telescope, and it's anticipated for launch in 2018. The studies we're doing with ALMA now are allowing us to get to a jumpstart on that whole quest.

TKF: In a way, what you have is the ultimate zoom camera, letting you see details about the early universe once unimaginable. Now that you've seen what ALMA can do, what are your next steps?

MARRONE: I'd really like to push ALMA to its full potential and examine individual star-forming regions within these galaxies. One of our galaxies, at a redshift of 5.7, is forming stars at a rate per unit area that’s as high as anything we've ever observed in the entire universe. ALMA is going to make it possible for us to pick that apart, to resolve the individual star-forming regions that are giving us those incredible starbursts.

VIEIRA: Now that we have the redshifts for these galaxies, we can dig deeper into the spectra of these galaxies to find out what they're made of; we can do chemistry with them. We have a sample of about 100 galaxies, and so what we want to do is get redshifts for all of them. Then we can map out the redshift distribution of these sources in an unbiased way. We'll be looking at individual spectral lines in detail, and examining the chemical makeup of these galaxies - even from region to region within them. Future studies also will help us answer other important questions, such as how they formed. Did they form through mergers, or through the slow accretion of gas? How many stellar generations reside in these galaxies?

These questions are all really exciting, and answering them is eventually going to change our view of the universe. Right now we've only taken the first step.

- Winter, 2013

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KICP Members: John E. Carlstrom
Scientific projects: South Pole Telescope (SPT)

by Marcus Woo, Steve Koppes, The University of Chicago News Office

When a batch of bright cosmic objects first appeared in maps in 2008 made with data from the South Pole Telescope, astronomers at the University of Chicago's Kavli Institute for Cosmological Physics regarded it only as an unavoidable nuisance.

The light sources interfered with efforts to measure more precisely the cosmic microwave background-the afterglow of the big bang. But the astronomers soon realized that they had made a rare find in South Pole Telescope's large survey of the sky. The spectra of some of the bright objects, which is the rainbow of light they emit, were inconsistent with what astronomers expected from the well-known population of radio galaxies.

Instead they looked like dust-enshrouded, star-forming galaxies. Such galaxies should be easily identified in infrared sky surveys, but there were no known counterparts for what the South Pole Telescope had found. They had to be extremely distant to avoid infrared detection, and therefore extremely luminous. Intrigued, the astronomers performed detailed follow-up imaging of the sources with the new Atacama Large Millimeter Array (ALMA) in Chile's Atacama Desert. These observations show the dust-filled galaxies were bursting with stars much earlier in cosmic history than previously thought.

Joaquin Vieira, now a postdoctoral scholar at the California Institute of Technology, leads a team that will report the discovery in the March 13 issue of the journal Nature and in two other papers that will appear in the Astrophysical Journal.

"We have been eagerly waiting for ALMA to be ready so we could conduct these observations," said Vieira, MS'05, PhD'09, who based his doctoral research at UChicago on the discovery of the extragalactic sources. "The sources we discovered with the South Pole Telescope were so far in the southern sky that no telescopes in the Northern Hemisphere could observe them. We are very privileged to be among the first astronomers to use ALMA."

Vieira has supported the South Pole Telescope from the beginning, helping to build the telescope and its camera, said John Carlstrom, S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics at UChicago. "He's been involved from the ground up, or the ice up, if you will," said Carlstrom, who leads the SPT collaboration and is a co-author of the Nature paper.

Prodigious star production
The starburst galaxies produce stars at a prodigious rate, creating the equivalent of a thousand new suns annually. Vieira and his colleagues have found starbursts that were churning out stars when the universe was just a billion years old. Previously astronomers were unsure whether galaxies could form new stars so quickly at this very early point in the history of the universe.

Shining with the energy of a trillion suns or more, these newly discovered galaxies are observed as they were nearly 12 billion years ago, showing us a representative baby picture of the most massive galaxies in Earth's cosmic neighborhood today. "The more distant the galaxy, the further back in time one is looking, so by measuring their distances, we can piece together a timeline of how vigorously the universe was making new stars at different stages of its 13.7-billion-year history," Vieira said.

The astronomers found dozens of these galaxies with the South Pole Telescope, a 10-meter dish in Antarctica that surveys the sky in millimeter-wavelength light (situated between radio and the infrared on the electromagnetic spectrum). The team then took a more detailed look using ALMA in Chile. "These aren't normal galaxies," Vieira said. "They're forming stars at an extraordinary rate when the universe was very young - we were very surprised to find galaxies like this so early in the history of the universe."

The new observations represent some of ALMA's most significant scientific results yet, Vieira said. "We couldn’t have done this without the combination of the South Pole Telescope and ALMA," he added. "ALMA is so sensitive, it is going to change our view of the universe in many different ways."

The astronomers used only 16 of 66 dishes that will eventually come online for ALMA, which is the most powerful telescope observing in millimeter and sub-millimeter wavelengths. ALMA began observing last year.

ALMA data analysis
Analysis of the ALMA data showed that more than 30 percent of the new galaxies existed just a billion years after the big bang. Only nine such galaxies were known previously. The number of such galaxies now has nearly doubled, providing valuable data that will help other researchers constrain and refine computer models of star and galaxy formation in the early universe.

Vieira's team directly determines the distance of these dusty starburst galaxies from emission from their gas and dust itself. Astronomers previously had to rely on a cumbersome combination of indirect optical and radio observations using multiple telescopes to study the galaxies. But ALMA's unprecedented sensitivity and ability to measure spectra enabled the astronomers to make their observations and analyze them directly in one step. As a result, the new distances are more reliable and represent the best sample yet of this population of early galaxies.

The unique properties of these objects also enabled the measurements. First, the observed galaxies happened to be gravitationally lensed - a phenomenon predicted by Einstein in which another galaxy in the foreground bends the light from the background galaxy like a magnifying glass. This lensing effect makes the background galaxies appear brighter, cutting the amount of telescope time needed to observe them by 100 times.

Second, the astronomers took advantage of a fortuitous feature of these galaxies' spectra. Normally, more distant galaxies appear dimmer. But it turns out that the expanding universe shifts the emitted spectra in such a way that the light we receive at millimeter wavelengths is not diminished for sources that are more distant from us. Consequently, the galaxies appear just as bright in these wavelengths no matter their distance.

The new results represent approximately a quarter of the total number of sources that Vieira and his colleagues discovered with the South Pole Telescope. They anticipate finding more of the dusty starburst galaxies and expect some to be from even earlier times in the universe as they continue analyzing their data.

UChicago scientists contributing to the March 13 Nature paper are faculty members John Carlstrom, Mike Gladders and Steve Meyer; senior researchers Bradford Benson, Clarence Chang, Tom Crawford and Kathryn Schaffer; associate fellows Will High, Stephen Hoover, Ryan Keisler and Tom Plagge; associate Steve Padin; research associate Keren Sharon; and graduate students Lindsey Bleem, Monica Mocanu, Tyler Natoli and Kyle Story.

The South Pole Telescope is funded primarily by the National Science Foundation's Office of Polar Programs. Partial support also is provided by the NSF-funded Physics Frontier Center of UChicago's Kavli Institute for Cosmological Physics, the Kavli Foundation, and the Gordon and Betty Moore Foundation.

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KICP Members: Bradford A. Benson; John E. Carlstrom; Clarence L. Chang; Thomas M. Crawford; Michael D. Gladders; Fredrick W. High; Stephen Hoover; Ryan Keisler; Stephan S. Meyer; Steve Padin; Tom Plagge; Kathryn K. Schaffer
KICP Students: Lindsey E. Bleem; Monica Mocanu; Tyler Natoli; Kyle Story
Scientific projects: South Pole Telescope (SPT)

by Steve Koppes, The University of Chicago News Office

The National Aeronautics and Space Administration has awarded $4.4 million to a collaboration of scientists at five United States universities and NASA’s Marshall Space Flight Center to help build a telescope for deployment on the International Space Station in 2017.

The U.S. collaboration is part of a 13-nation effort to build the 2.5-meter ultraviolet telescope, called the Extreme Universe Space Observatory. UChicago Prof. Angela Olinto leads the U.S. collaboration. The telescope will search for the mysterious source of the most energetic particles in the universe, called ultra high-energy cosmic rays, from the ISS's Japanese Experiment Module. The source of these cosmic rays has remained one of the great mysteries of science since physicist John Linsley discovered them more than 50 years ago. These cosmic rays consist of protons and other subatomic scraps of matter that fly through the universe at almost light speed.

"The science goal is to discover the sources of ultra high-energy cosmic rays by observing their traces in the atmosphere looking 248 miles from the ISS down to the surface," said Olinto, professor in astronomy & astrophysics at the University of Chicago's Kavli Institute for Cosmological Physics. In addition to leadership from UChicago, the U.S. collaboration includes scientists at the Colorado School of Mines, University of Alabama in Huntsville, Vanderbilt University, University of California at Berkeley, University of California Los Angeles, University of Wisconsin-Milwaukee, and the Marshall Space Flight Center.

A subset of the U.S. institutions will use the NASA grant to build lasers, flashers and monitoring equipment that will be used to calibrate the telescope’s optics from 20 locations around the globe as the ISS passes overhead.

Billions of particles
Ultra high-energy cosmic rays may come from supermassive black holes at the centers of nearby galaxies, or perhaps they are decaying particles left over from the big bang. These rays hit the atmosphere with the energy of a tennis ball traveling at 167 miles an hour. This impact produces a giant cascade of many tens of billions of secondary particles that previously have been observed only from Earth-based detectors.

UChicago has a long history of cosmic-ray research, including the Pierre Auger Observatory, the largest cosmic-ray detector ever built. Auger conducted cosmic ray research at UChicago in 1942, launching hot air balloon experiments from the former site of the University's Stagg Field.

UChicago Nobel laureate James Cronin initiated the Auger project with Alan Watson of the University of Leeds in the early 1990s. They built the observatory in Argentina in collaboration with scientists from 19 countries, who shared construction costs for the $50 million observatory. When Auger's construction was completed in 2008, the observatory consisted of a grid of electronic instruments that covered 3,000 square kilometers, an area more than half of the size of Delaware.

The Auger Observatory began collecting data in 2004. "We have solved many open questions from last century, but we didn't find the source of the highest-energy cosmic rays," Olinto said. The most useful data occur at the very highest energies. Auger detects approximately two of these highest-energy events every month.

But it takes a long time to collect enough of these events to make a map of the sky that indicates more of them are coming from one direction than another. "I wanted to go the next step, which is to make something 10 times bigger than Auger," Olinto said.

Particle flashes
Auger combines two techniques for observing cosmic rays. One technique consists mostly of large plastic water tanks, which serve as ground detectors that measure the shape of the shower. Spaced at one-mile intervals, the tanks occasionally intercept a particle from the atmospheric cascade generated by cosmic rays. The particles produce a flash as they cross from air into water. Electronics in the dark tanks detect the light and radios the information to a central station.

The second technique involves four infrared telescopes that detect ultraviolet light emissions generated in the atmosphere by cosmic rays. "You not only see the fluorescence on the ground, but you see the whole shower developing on the atmosphere," Olinto explained.

The Auger telescopes look straight up to the top of the atmosphere, approximately 40 kilometers (24.8 miles) high. "If you go to the International Space Station with the exact same technique and you look down, you can see a lot more of the atmosphere because now you're 400 kilometers up," Olinto said. "With a 60-degree opening angle, which we are designing, you can see instantaneously a hundred times the Auger area."

Olinto views the Extreme Observatory as the first step toward using the entire Earth atmosphere for studying subatomic particle interactions at energies far exceeding what the most powerful man-made accelerator at the Large Hadron Collider can currently produce. "In my opinion, it's the way to the future," she said.

For more information see http://jem-euso.uchicago.edu/.

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by Jonathan Amos, BBC News Science & Environment

The scientist leading one of the most expensive experiments ever put into space says the project is ready to come forward with its first results.

The Alpha Magnetic Spectrometer (AMS) was put on the International Space Station to survey the skies for high-energy particles, or cosmic rays.

Nobel Laureate Sam Ting said the scholarly paper to be published in a few weeks would concern dark matter.

This is the unseen material whose gravity holds galaxies together.

Researchers do not know what form this mysterious cosmic component takes, but one theory points to it being some very weakly interacting massive particle (or Wimp for short).

Although telescopes cannot detect the Wimp, there are high hopes that AMS can confirm its existence and describe some of its properties from indirect measures.

The imminent publication in an as yet undetermined journal will detail the progress of that investigation.

The Massachusetts Institute of Technology professor said the project he first proposed back in the mid-1990s had now reached an important milestone.

"We've waited 18 years to write this paper, and we're now making the final check," he told reporters.

"I would imagine in two or three weeks, we should be able to make an announcement.

"We have six analysis groups to analyse the same results. Physicists as you know - everybody has their own interpretations, and we're now making sure everyone agrees with each other. And this is pretty much done now."

Sam Ting was speaking here in Boston at the annual meeting of the American Association for the Advancement of Science (AAAS).

$2bn machine to 'probe the unknown'
His $2bn machine was taken up to the ISS in 2011 - on the final mission of Shuttle Endeavour.

The seven-tonne experiment holds a giant, specially designed magnet that bends the paths of particles that fall on it.

The way they bend reveals their charge, a fundamental property that, together with information about their mass, velocity and energy, garnered from a slew of detectors, tells scientists precisely what they are dealing with.

Prof Ting said that in its first 18 months of operation, AMS had witnessed 25 billion particle events.

Of these, nearly eight billion were fast-moving electrons and their anti-matter counterparts, positrons.

Colliding and annihilating Wimps ought to produce showers of these electrons and positrons. And it is by measuring the ratio of the latter to the former, and the behaviour of any excess across the energy spectrum, which may provide a way into the dark matter problem.

"The smoking gun signature in the positron to electron ratio is a rise and then a dramatic fall. That is the key signature for the dark matter annihilation in our galaxy's halo," observed Prof Michael Turner from the Kavli Institute for Cosmological Physics, University of Chicago. Prof Turner is not part of the AMS Collaboration.

"Also in this energy regime, is there anisotropy? Do the positrons come from a fixed direction or all directions?" Prof Ting pondered to the BBC.

"Dark matter is supposed to be everywhere. So if we see the positrons coming from a particular direction, it means astrophysics like a pulsar (a type of neutron star) is responsible for the signal, not dark matter."

The AMS paper will report the positron-electron ratio in the mass range of 0.5 to 350 Gigaelectronvolts. This covers territory at the top end where some other experiments have already reported tantalising hints of dark matter.

Prof Turner said science was closing in on its quarry.

He predicted the next few years would be remembered as the "decade of the Wimp", and looked forward to dark matter's properties being exposed via a number of investigation strands that included Wimp production at the Large Hadron Collider (LHC).

"Theory says that this particle might weigh somewhere between 30, 40 and 300 times what the proton does, so somewhere between 30 and maybe 1,000 GeV.

"The LHC can produce particles of that mass, Sam Ting's AMS detector can see particles of that mass annihilating, and then the detectors deep underground are also sensitive to particles of this mass.

"If we get very lucky, if Santa answers our wish-list, we could get a triple signature of the dark matter particle, by seeing the annihilations, by directly detecting it, by producing it at the LHC - all three of these methods are sensitive across the same mass range."

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BBC World Service

BBC World Service gives a tour "inside" the DarkSide-50 detector. The experiment, ready to be assembled at National Laboratory of Gran Sasso, is searching for Dark Matter interactions in a low background two-phase Time Projection Chamber featuring 50 kg of Underground Argon as the sensitive target. To further suppress the background the liquid argon detector will be fully immersed in a liquid scintillator and surrounded by a large water Cherenkov detector working as active vetoes. The commissioning of the detector is expected to start in about two weeks.

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KICP Members: Luca Grandi
Scientific projects: Depleted Argon cryogenic Scintillation and Ionization Detection (DarkSide)

Kavli Foundation News

As the search for dark matter intensifies, the Kavli Institute for Cosmological Physics at the University of Chicago and the National Academy of Sciences organized a colloquium that brings together cosmologists, particle physicists and observational astrophysicists - three fields now united in the hunt to determine what is dark matter.

DARK MATTER IS ONE OF THE BIGGEST MYSTERIES IN MODERN PHYSICS. We believe it makes up about 23 percent of the mass-energy content of the universe, even though we don't know what it is or have yet to directly see it (which is why it's called "dark"). So how can we detect it and when we do, what will it reveal about the universe?

In mid-October, more than 100 cosmologists, particle physicists and astrophysicists gathered for a meeting called Dark Matter Universe: On the Threshold of Discovery at the National Academy of Sciences' Beckman Center in Irvine, CA. Their goal: to take stock of the latest theories and findings about dark matter, assess just how close we are to detecting it and spark cross-disciplinary discussions and collaborations aimed at resolving the dark matter puzzle. Following the meeting, The Kavli Foundation met with three leading participants and organizers of the meeting:
* Michael S. Turner - Rauner Distinguished Service Professor and Director of the Kavli Institute for Cosmological Physics at the University of Chicago.
* Edward "Rocky" Kolb - Professor in the Department of Astronomy and Astrophysics at the University of Chicago, where he is also a member of the Enrico Fermi Institute and the Kavli Institute for Cosmological Physics.
* Maria Spiropulu - Professor of Physics at California Institute of Technology who also works on experiments at the Large Hadron Collider, and a former fellow at the Enrico Fermi Institute.

The following is an edited transcription of the discussion.

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THE KAVLI FOUNDATION: This meeting brought together theoretical cosmologists, observational astrophysicists and experimental particle physicists. Why this mix of researchers and why now?

MICHAEL TURNER: Figuring out what is dark matter has become a problem that astrophysicists, cosmologists and particle physicists all want to solve, because dark matter is central to our understanding of the universe. We now have a compelling hypothesis, namely that dark matter is comprised of WIMPs (Weakly Interacting Massive Particle), particles that don't radiate light and interact rarely with ordinary matter. After decades of trying to figure out how to test the idea that dark matter is made up of WIMPs, we have three ways to test this hypothesis. Best of all, all three methods are closing in on being able to either confirm or falsify the WIMP. So the stars have truly aligned.

ROCKY KOLB: The title to this meeting is a great answer to your question. It's "On the Threshold of Discovery," and it could happen within the next one or two years. It's so important to get the different communities here - experimentalists working at colliders, people analyzing gamma ray data from space, and those involved in direct detection.

TKF: So dark matter is a mystery that everyone wants to solve.

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Michael Turner - Director of the Kavli Institute for Cosmological Physics (KICP) at the University of Chicago, and a theoretical cosmologist trained in both particle physics and astrophysics. Dr. Turner coined the term "dark energy" and helped establish the interdisciplinary field that combines cosmology and elementary particle physics. His research focuses on the earliest moments of creation, and he has made important contributions to inflationary cosmology, particle dark matter and structure formation, the theory of big bang nucleosynthesis, and the nature of dark energy.

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TURNER: Ten years ago, I don't think you would've found astronomers, cosmologists, and particle physicists all agreeing that dark matter was really important. And now, they do. And all of them believe we can solve the problem soon. It's wonderful listening to particle physicists explain the evidence for dark matter, and vice versa -astronomers explaining WIMPs as dark matter. At this meeting nobody said, "Oh, I don't really believe in the evidence. Nor did anyone say, "Yikes - a new form of matter. That's crazy."

MARIA SPIROPULU: One important thing we've seen at this meeting is a crossing of professional boundaries that have separated researchers in many different fields in the past. These boundaries have been strict. Cosmologists, astrophysicists and particle physicists, however, have now really started talking to one another about dark matter. We're only beginning and our language - the way speak to each other - is not yet settled so that we completely understand each other; but we are on the threshold of discovering something very important for all of us. This is critical because cosmologists and particle physicists have talked for a long time about how the very big and very small might be linked. And while the particle physicists study the very small with colliders, cosmologists study the galaxies and billions and billions of stars that make up the large-scale structure we see in the universe.

KOLB: Ten years ago, it was "Call me maybe" and now it's ...

TURNER: "Let's do lunch."

SPIROPULU: Yes, it's, "Let's do lunch and talk physics."

TURNER: I do want to make one point: the convergence of inner space and outer space really started in the 1980s. Back then it began with the origin of the baryon asymmetry, the monopole problem and dark matter to a lesser extent. Particle physicists agreed that dark matter was a real problem but said, "The solution could be astrophysics - faint stars, 'Jupiters', black holes and the like." It's been a long road to get to where we are now, namely where we all agree that the most compelling solution is particle dark matter. And even today, the different fields are still, in a sense, getting to know one another.

TKF: Let's cover a few basics. Why is the question of dark matter important?

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"Rocky" Kolb - A professor of Astronomy & Astrophysics at the University Of Chicago, "Rocky" Kolb is a member of the Enrico Fermi Institute and the Kavli Institute for Cosmological Physics, studies the application of elementary-particle physics to the very early Universe. He is the co-author with Michael Turner of The Early Universe, the standard textbook on particle physics and cosmology.

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KOLB: As cosmologists, one of our jobs is to understand what the universe is made of. To a good approximation, the galaxies and other structures we see in the universe are made predominantly of dark matter. We have concluded this from a tremendous body of evidence, and now we need to discover what exactly is dark matter. The excitement now is that we are closing in on an answer, and only once in the history of humans will someone discover it. There will be some student or postdoc or experimentalist someplace who is going to look in the next 10 years at their data, and of the seven or so billion people in the world that person will discover what galaxies are mostly made of. It's only going to happen once.

TURNER: The dark matter story started with fragmentary evidence discovered by Fritz Zwicky, a Swiss American. He found that there were not enough stars in the galaxy clusters he observed to hold them together. Slowly, more was understood and finally dark matter became a centerpiece of cosmology. And now, we have established that dark matter is about 23 percent of the universe; ordinary matter is only 4.5 percent; and dark energy is that other 73 percent - which is an even bigger puzzle.

Nothing in cosmology makes sense without dark matter. We needed it to form galaxies, stars and other structures in the Universe. And so it's absolutely central to cosmology. We also know that none of the particles known to exist can be the dark matter particle. So it has to be a new particle of nature. Remarkably, our most conservative hypothesis right now is that the dark matter is a new form of matter - out there to be discovered and to teach us about particle physics.

---

Maria Spiropulu - A Professor of Physics at the California Institute of Technology (Caltech) in Pasadena, CA. An experimental particle physicist, Spiropulu is interested in the search for dark matter at the Large Hadron Collider at CERN (The European Organization for Nuclear Research), and questions about dark matter that cut across particle physics, astrophysics and cosmology. Spiropulu was previously a senior physics researcher in the Physics Department at CERN from 2004-2012. She was also an Enrico Fermi Fellow from 2001-2004.

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SPIROPULU: I just want to say one thing. The phenomenon of dark matter was discovered from astronomical observations. We know that galaxies hang together and they don't fly apart, and it's the same with clusters of galaxies. So we know that we have structure in the universe. Whatever it is that keeps it there, in whatever form it is, we call that dark matter. This is the way I teach it to undergraduates. It's a fantastical story. It's still a mystery and so it’s "dark," but the universe and its structures - galaxies and everything else we observe in the macroscopic world - are being held together because of it.

TKF: Dark matter is often described in the media as something that is inferred because of its gravitational effects on ordinary matter. But the case for dark matter is much more expansive than that, as astrophysicist Jeremiah [Jerry] Ostriker from Princeton University said at this meeting.

TURNER: Absolutely. Dark matter is absolutely central to cosmology and the evidence for it comes from many different measurements: the amount of deuterium produced in the big bang, the cosmic microwave background, the formation of structure in the Universe, galaxy rotation curves, gravitational lensing, and on and on. Jerry said that as far as he is concerned, the dark matter problem has been solved. And that's because this idea that dark matter is just a swarm of particles that are very shy, that rarely interact with ordinary matter and then only weakly, works perfectly. And at the end of his talk, he said, as a kind of footnote: "By the way, I would be interested in knowing what the dark matter is." This is a testimony to how central dark matter is to cosmology and culturally to how particle physicists and astrophysicists look at dark matter differently. Dr. Gross, the particle physicist, wanted to know what dark matter is made of.

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The Search for Dark Matter
What is dark matter? We don't know, but cosmologists, astrophysicists and experimental particle physicists say they are closing in on an answer. Read a short explanation of what scientists consider the leading candidate, as well as the methods being used to detect dark matter.

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TKF: So for Dr. Ostriker, knowing exactly what dark matter is is less important than the work done already - measuring its gravitational influence on ordinary matter, estimating how much of the universe is made from it, and affirming that what we do know about it fits with the standard model of cosmology.

TURNER: That was Jerry's point, yes. There is five times more dark matter than ordinary matter, and its existence allows us to understand the history of the universe beginning from a formless particle soup until where we are today. If you said, "You no longer have dark matter," our current cosmological model would collapse. We would be back to square one.

TKF: Dr. Ostriker also argued that we should be open to dark matter being a variety of fundamental particles and not only WIMPs. Other possibilities could be neutrinos and axions.

TURNER: Because he doesn't care what it is. They all work equally well. The flip side is that cosmology tells us little about dark matter except it is cold.

TKF: Do they all work equally well for each of you?

KOLB: Well, for cold dark matter - which is made from particles that move slowly compared with the speed of light, and is the kind needed for forming galaxies and galaxy clusters - they all work equally well. The thing about the WIMP, as opposed to some of these other candidate particles, is that it's a very compelling possibility we can test right now. So we don't have to wait for the next 30 years or the next century, as we might if we were trying to detect another type of hypothesized particle. We don't have to build an accelerator larger than LHC.

It's a magical moment when astronomers, astrophysicists, string theorists, particle experimentalists and cosmologists get together because they all have a common purpose. There is a common problem that excites them.

TKF: What makes you most optimistic that we're on the threshold of discovery?

KOLB: First of all, the hypothesis that dark matter is made up of WIMPs - and that it was produced by normal particles, say quarks, in the early universe - is an amazing achievement all by itself. Independent of a lot of the details of what goes on there and exactly how that happens, we expect that you should be able to reverse things and produce WIMPs in particle accelerators. We also expect they should be annihilating today in the galaxy, which we should be able to detect indirectly. Now, it's another issue who will be the first to find WIMPs. It's possible that it will be another 30 years before we do that, but we should be able to make a detection - whether it's direct or indirect.

SPIROPULU: With the Large Hadron Collider, and before that the Tevatron collider, we have been chasing and targeting the dark matter candidate. For us, the optimism is because the LHC is working and we're collecting a lot of data. In the standard model of particle physics, when we enlarge it to help explain how the universe began and evolved, we have a story that is a mathematical story. It's very good at describing how we can have dark matter. And if the mathematics accurately describes reality, then the LHC is now achieving the energies that are needed to produce dark matter particles.

Getting to these high energies is critical, and we are even going to higher energies. When we were building the standard model of particle physics, we kept saying that the next particle discovery that we predicted was "right around the corner." In other words, we were not, and we are not, flying in the dark. We are guided by a huge amount of data and knowledge, and while you might think there are infinite possibilities of what can happen, the data actually points you to something that is more probable. For example, we have found the Higgs-like particle, but that was predicted. So the next big step for this edifice of knowledge is to find something that will look like supersymmetry - a hypothesis that, if true, offers a perfect candidate for dark matter. We call it a miracle, because the mathematics works. But the way nature works, in the end, is what you see in the data. So if we find it, there is no miracle.

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"Cosmologists, astrophysicists and particle physicists have now really started talking to one another about dark matter. We're only beginning and our language - the way speak to each other - is not yet settled... but we are on the threshold of discovering something very important for all of us. - Maria Spiropulu

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TURNER: These dark matter particles, or WIMPs, don't interact with ordinary matter often. It's taken 25 years to improve the sensitivity of our detectors by a factor of a million, and now they have a good shot at detecting the dark matter particles. Because of the technological developments, we think we are on the cusp of a direct detection.

Likewise for indirect detection. We now have instruments like the Fermi satellite (the Fermi Gamma-ray Space Telescope) and the IceCube detector (the IceCube Neutrino Observatory at the South Pole) that can detect the ordinary particles (positrons, gamma rays or neutrinos) that are produced when dark matter particles annihilate, indirectly allowing dark matter to be detected. IceCube is big enough to detect neutrinos that are produced by dark matter annihilations in the sun.

TKF: A few people over the past two days have said the dark matter particle might not be detectable.

TURNER: For many of us, for 20 to 30 years, this idea that dark matter is part of a unified theory has been our Holy Grail and has led to the WIMP hypothesis and the belief that the dark matter particle is detectable. But there's a new generation of physicists that is saying, "Well, there's an alternative view. Dark matter is actually just the tip of an iceberg of another world that is unrelated to our world. And I cannot even tell you about that world. There are no rules for that other world, at least that we know of yet." Sadly, this point of view could be correct and might mean the solution to the dark matter problem is still very far away. That is what led Jerry to say that discovering what dark matter actually is could be 100 years away.

TKF: Michael Witherell, Professor of Physics at the University of California, Santa Barbara, also said that nature doesn't guarantee an observation.

TURNER: Also true. But we have the WIMP hypothesis and it is falsifiable. And there's a good chance it's true. A "good chance" in this business means 10 percent or 20 percent. But when you’re trying to solve a problem of this magnitude, if you have a 10-20 percent chance, I say let's double down on that.

TKF: When do you predict we'll detect WIMPs?

KOLB: It's easy to say, "A decade." LHC is turning on now. It'll be another year or so before they are at full energy, and they may run a couple of years to accumulate data. Meanwhile, the Fermi satellite is in space making observations. And then we have experiments underground: a detection may come with Xenon100, one dark matter experiment now underway in central Italy, or some successor to Xenon100.

TKF: And programs like LUX, the Large Underground Xenon dark matter experiment in South Dakota, are just coming online.

KOLB: In ten years, if there is no indication of supersymmetry or a WIMP - either from direct detection or indirect detection searches - then there is going to be a sea change. Now, there is not going to be one experiment announcement that says, "OK, let's look at something else." But if ten years from now there is no evidence, then we are going to other possibilities. You could not have said that ten years ago, or even five years ago. Today, I think you can say that.

TKF: Because we have so much work behind us and have already eliminated numerous possibilities.

KOLB: As in Ghostbusters, we have the tools. We have the talent.

SPIROPULU: I think it's fair to say the discovery is "around the corner." If we continue with exclusions, then we have to come up with better ideas. We are doing all this because we want to characterize dark matter. We are not just saying, "It is dark matter." We don't want to just say, "The universe is." We want to know exactly what it is made of. We want to know the dynamics and what it involves. A lot of work is ahead of us. Somebody said that it's not going to be as easy as finding the Higgs. Well, finding the Higgs was extremely nontrivial. Of course, once we find it, it goes in the pool of knowledge and then you say, "Well, it was easy."

---

"[W]e need to discover what exactly is dark matter. The excitement now is that we are closing in on an answer, and only once in the history of humans will someone discover it." - Rocky Kolb

---

TKF: Painting a picture for the general public about how incredible it would be to discover a WIMP is challenging. How do you convey just how sensitive this measurement would be?

TURNER: I keep saying these particles are very shy. Here's one way to think about this: if you had 100 kilograms of material, one of these shy particles - one of these WIMPS - would interact with that 100 kg once in a year or even less often. So you really have to build very sensitive detectors. Because of the cosmic rays and other particles that light up your detector and obscure the WIMP signal you're looking for, you have to put WIMP detectors underground. And even underground you still get natural radioactivity clouding your signal, so you have to discriminate against that as well.

Now, we also expect there's a seasonal modulation in the dark matter signal as the Earth orbits the sun through the sea of dark matter particles that permeate space. The modulation signal is expected to be only a few percent of the rare, dark-matter signal I talked about a minute ago. We do have the equipment in place to make these detections, but we just need Nature to cooperate.

KOLB: It's a fantastical story. One hundred years ago, if I told you that we are surrounded by these invisible particles and they're passing through us - you don't feel them yet they form the entire structure of the universe - you would have locked me up.

TKF: Do any of you expect that learning about dark matter will help us also learn about the other big mystery in cosmology - dark energy?

KOLB: Possibly nothing. It depends on what the answer will be. It is possible it won't shed any light on the nature of dark energy.

TURNER: There are two views. One is a conservative view, which is that dark matter is just made up of particles that don't give off light. It's just particles that happened to be more important than the stuff that we are made out of, which we only discovered in the past 70 years. And dark energy is a new problem that is unrelated.

TKF: And the only thing they share at this point is being unknown?

TURNER: That's right. The conservative point of view is that dark energy is unrelated to dark matter. Recall, dark energy is the stuff that is causing the universe to speed up. This is the simple view where we are solving problems one at a time.

A more radical view which we heard about at this meeting from Erik Verlinde (from the University of Amsterdam) is, "You know, guess what? Don't you guys get it? The two of them are related. It has nothing to do with particles. It's something much, much bigger. The two are related and are pointing to a much richer explanation. You are trying to explain things in a simple-minded way: dark matter particles and dark energy. Just like Ptolemy's epicycles (the epicycles of Claudius Ptolemy, a Greek astronomer who lived in Alexandria, Egypt under Roman rule, is a false construction of an Earth-centered universe, specifically describing the observed retrograde motion of planets), a desperate attempt to make a wrong hypothesis work.

And so those are the two extremes. One is that we are just about to solve dark matter and then we will go on to dark energy and they're probably not related; the other is that together, they make this big flashing sign: You guys really need to sit down and reconsider the whole framework.

SPIROPULU: I think it's worth noting that the dark sector (i.e. dark matter and dark energy) has to do with gravity. They are linked via gravity. Gravity is a force that in particle physics we have not been able to put together with the rest of the forces. Somehow, if you could stand outside the universe - that's an absurd statement, of course - but stand outside it and see how everything relates, you could say something about the dark sector and gravity.

TURNER: You're right that gravity could be the connector, because in cosmology and astrophysics gravity is the most important force. In particle physics, it's the least important force. Consequently particle physicists are just getting around to worrying about it, and in cosmology we mostly worry about gravity. And so now, we have come together because of a common interest in gravity - gravity revealed to us through dark matter and dark energy.

SPIROPULU: Here we are, with dark matter between us. It's a beautiful story of how we are trying to solve the problems, the challenges of characterizing our physical world.

KOLB: Dark matter holds together the galaxies. It holds together cosmologists and particle physicists.

TURNER: We know that Einstein didn't get the last word on gravity, because his theory doesn't have quantum mechanics in it. And so any problem that involves gravity, you are thinking, nervously and excitedly, that this could be the clue to the grander theory of gravity.

KOLB: I don't think the general public appreciates that we would love to find something wrong with what we think about the universe, about the laws of nature. And that's because it points the way toward new discoveries. I don't think most people work that way, thinking that, "Boy, I would love to be shown that I'm wrong about something that I really thought was true for 30 years or 100 years."

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"[T]he universe is vast....but we are at a point in time where we really think we understand it and that we can identify what dark matter is. ...This is the time to be a dark cosmologist." - Michael Turner

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TURNER: We want new puzzles.

SPIROPULU: Always. And I have to say that in particle physics, there is a list of experiments and projects that have been built in the past 30 years that did not find what they were built for. None. They found other things, other important things. It's incredible. One example of this is the Hubble Space Telescope, which has revealed more about the universe than we ever could have imagined when it was conceived. The series of deep field images of the very distant universe, which has given us glimpses of the earliest galaxies, is just one example of this. So, when you write a proposal for something and you say what you are building it for, and you get the money and you go and build it and you find something completely unexpected - Wow. Our physical world is surprising. And it's very surprising that we can get it, even at the level we do. Or that we can do the experiments that we do.

TURNER: I think the universe is vast. It's often beyond the reach of our instruments and our minds, but we are at a point in time here where we really think we understand it and that we can identify what dark matter is. We have an accounting of the universe and a compelling hypothesis for dark matter. It is not unexpected that the younger generation of scientists wants a more radical solution to dark matter. The older generation developed the WIMP hypothesis, and this is our solution and we want to see it come true. The younger generation wants the excitement of solving a problem.

TKF: Would any of you trade this point in time with another in the history of physics?

KOLB: No, no. For dark matter, I think this is the time. I can't see everything converging at another time like it is now.

TURNER: This is the time to be a dark cosmologist.


- Fall 2012

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KICP Members: Edward W. Kolb; Michael S. Turner

by Steve Koppes, William Harms, The University of Chicago News Office

Four University of Chicago faculty members were elected as fellows of the American Association for the Advancement of Science, the organization announced on Nov. 29.

The UChicago fellows are: Anthony Kossiakoff, the Otho S.A. Sprague Professor of Biochemistry and Molecular Biology and the Institute for Biophysical Dynamics; Angela Olinto, Professor in Astronomy & Astrophysics; Steven Shevell, the Eliakim Hastings Moore Distinguished Service Professor in Psychology and Ophthalmology & Visual Science; and Melvyn Shochet, Professor in Physics.

In all this year, 702 scholars were named AAAS fellows for their scientifically or socially distinguished efforts to advance science or its applications. The new fellows will be presented with an official certificate and pin at the AAAS Fellows Forum during the 2013 AAAS annual meeting in Boston. The AAAS is an international organization that promotes scientific understanding through many programs, including publication of the prestigious journal Science.

Angela Olinto
Olinto is being recognized for her distinguished contributions to the field of astrophysics, particularly exotic states of matter and extremely high-energy cosmic ray studies at the Auger Observatory.

Olinto's research interests span theoretical astrophysics, particle and nuclear astrophysics, and cosmology. She has focused much of her work on understanding the origins of the highest energy cosmic rays and the ultra-compressed core of matter in neutron stars. Ultra-high-energy cosmic rays enter the atmosphere with so much energy that they produce a giant cascade of many tens of billions of secondary particles, which can be observed by large detectors such as the Auger Observatory.

Olinto now leads the Japanese Experiment Module-Extreme Universe Space Observatory mission to observe these ultra-energy particles from the International Space Station.

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KICP Members: Angela V. Olinto
Scientific projects: Pierre Auger Observatory (AUGER)

AMNH Science Bulletin

The icy South Pole desert is a harsh and desolate landscape in which few life-forms can flourish. But the extreme cold and isolation are perfect for astronomical observations. Taking advantage of the severe conditions, scientists are using the new South Pole Telescope - the largest ever deployed in Antarctica - to observe the oldest light in the Universe, the cosmic microwave background (CMB).

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KICP Members: Bradford A. Benson; John E. Carlstrom; Randall H. Landsberg
Scientific projects: South Pole Telescope (SPT)

by Lisa La Vallee, The University of Chicago News Office

Five teams of University of Chicago and Fermi National Accelerator Laboratory researchers, including one team with an Argonne National Laboratory member, recently received $375,000, collectively, in Strategic Collaborative Initiative seed grants from UChicago. Three of the five teams received second-year funding.

The FY 2012 recipients include:
* "Simulating the Universe with Realistic Physics" (Year 2) UChicago investigator Andrey Kravtsov, Associate Professor in Astronomy and Astrophysics, and Fermilab investigator Nickolay Gnedin, Scientist I in the Theoretical Astrophysics Group
* "Understanding Ultrahigh Quality Factor Accelerator Cavities in the Quantum Regime" (Year 2) UChicago investigator David Schuster, Assistant Professor in Physics, and Fermilab investigator Lance Cooley, Scientist in the Superconducting Materials Department
* "A New Photodetection System for PET Imaging Using Silicon Photomultipliers" (Year 2) UChicago investigator Chin-Tu Chen, Associate Professor in Radiology, and Fermilab investigator Erik Ramberg, Scientist II in the Particle Physics Division
* "Optical Modulation with Wavelength Division Multiplexing from HEP Data Readout" UChicago investigator Mark Oreglia, Professor in Physics; Argonne investigator Robert Stanek, Physicist in the High Energy Physics Division; and Fermilab investigator Simon Kwan, Scientist II in the Computing Division
* "Development of Low Noise Electronics for the First Direct Dark Matter Search Using CCDs" UChicago investigator Paolo Privitera, Professor in Physics, and Fermilab investigators Juan Estrada, Scientist II in the Particle Physics Division and Gustavo Cancelo, Engineer IV in the Computing Division

The Strategic Collaborative Initiatives Program began in 2005, when the University renewed its contract with the DOE to manage Argonne. It includes collaborative research projects, strategic joint appointments and joint institutes. The University extended the program to Fermilab when it became co-manager of the lab in 2006.

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KICP Members: Nickolay Y. Gnedin; Andrey V. Kravtsov; Paolo Privitera

by Stephanie Sunata, Medill Reports

It sits about two miles above sea level on an icy shelf at the most southern part of the globe. It probes microwaves from the farthest points in space. It surveys the southern sky and scientists hope it will help answer some of the universe's biggest questions.

The South Pole telescope is one of the pivotal tools scientists use to study the universe. It explores the enigmas of dark energy and was the topic of cosmologist John Carlstrom's recent public presentation at the School of the Art Institute of Chicago.

Carlstrom, professor of astronomy and astrophysics at the University of Chicago, uses the South Pole telescope to study the early universe and wants to make his research accessible to everyone.

"If you do your science and never share it, what's the point?" Carlstrom said.

At the talk Thursday, Carlstrom shared the construction process of the telescope and gave an overview of the mysteries it's trying to solve to an audience of about 100 people.

The telescope aimed at the heavens from Antarctica focuses on the edge of space where traces remain from when the Big Bang was plasma that radiated visible light, Carlstrom told the audience.

As the universe expanded, these light waves lengthened to microwaves during the 14-billion-light-year trip to reach Earth.

The South Pole telescope detects these microwaves that paint a picture of the early universe. The image contains temperature variations, and when analyzed, create a diminishing harmonic plot.

This is similar to the harmonics of musical instruments. Just as scientists can determine certain characteristics about a violin from plotting its acoustics, they can use the cosmic radiation graph to learn about early space.

"Our universe is ringing like a bell," Carlstrom said.

The telescope project also analyzes galaxy clusters, which act as a measurement tool in the battle between dark energy and the combination of dark matter and gravity, Carlstrom said.

Dark matter and gravity hold things together, but scientists believe the elusive dark energy pulls things apart. Galaxy clusters are sensitive to these opposing forces.

The clusters act as a rope in the tug-of-war in space. The South Pole telescope looks at this "rope" to see who's winning and, right now, it's dark energy, Carlstrom said.

This means the universe is not only expanding, but the expansion rate is accelerating due to dark energy.

"It's for everyone to appreciate," Carlstrom said in an interview. "It's your universe too."

Representatives from the Chicago Council on Science and Technology, one of the organizations that sponsored the talk, emphasized that part of scientific research means getting the public involved.

One effective way to do this is to hold public talks with scientists, said Andrea Poet, council public relations coordinator. "I think for people to hear about dark energy from a leading expert is exciting," Poet said.

Attendee Francesca Costa said she enjoyed Carlstrom's presentation, even though she studied humanities, not science.

Costa said Carlstrom's ideas were "clear" and "accessible" to a non-scientist and the concepts of cosmic microwaves and dark energy were interesting.

Even if she doesn't fully understand the science behind all the material, she believes the South Pole telescope project is important, Costa said.

Her husband, Bill Dague, a physics major at University of Chicago, said this research could answer an ages-old question: "How did it all get started?"

"Having an understanding of who we are and where we are is good overall for humanity," Dague said.

The presentation combined complex scientific data with simple analogies. Carlstrom tailored the speech to appeal to all types of people.

Though the topic of discussion was scientific, the venue was artistic.

Though he didn't decide on the location, Carlstrom said liked the idea of hosting the talk at an art school because both science and art require creativity.

An exhibit inpsired by the telescope project - created and designed by students at the school - helped exemplify the collaboration between art and science.

Instructor Bo Rodda led the Art Institute class that made the exhibit, which opened at the USA Science and Engineering Festival in Washington, D.C. earlier this year.

"Both artists and scientists are curious about the world," he said. Each discipline requires a person to make abstract ideas conceivable to the public, he added.

There were multiple pictures of the Antarctic, a touch-screen unit with information about the project and a station where people could put on a coat and boots worn in the freezing landscape.

The art students made the interactive exhibit with children in mind, Rodda said.

About a dozen teenagers attended Thursday's event, and Carlstrom spoke to some of them individually.

"It’s always really neat when you meet high school kids who are turned on by science," he said.

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KICP Members: John E. Carlstrom
Scientific projects: South Pole Telescope (SPT)

by Steve Koppes, The University of Chicago News Office

Scientists at the University of Chicago’s Kavli Institute for Cosmological Physics have great expectations for the newly operational Dark Energy Camera, which may significantly advance understanding of the mysterious force expanding the universe at an ever-accelerating rate. Two scientists at Fermi National Accelerator Laboratory will answer questions from viewers about the camera and what it's expected to reveal during a live Q&A and webcast from noon to 12:30 p.m. Friday, Oct. 12.

Participating in the event will be Brenna Flaugher, project manager for the Dark Energy Camera; and Joshua Frieman, director of the Dark Energy Survey and professor in astronomy & astrophysics at UChicago. The Dark Energy Survey is an international collaboration of more than 130 scientists from 27 institutions, including UChicago.

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KICP Members: Joshua A. Frieman
Scientific projects: Dark Energy Survey (DES)

by Ross Andersen, The Atlantic

Next month, one of the world's fastest supercomputers will run the largest, most complex universe simulation ever attempted.

Cosmology is the most ambitious of sciences. Its goal, plainly stated, is to describe the origin, evolution, and structure of the entire universe, a universe that is as enormous as it is ancient. Surprisingly, figuring out what the universe used to look like is the easy part of cosmology. If you point a sensitive telescope at a dark corner of the sky, and run a long exposure, you can catch photons from the young universe, photons that first sprang out into intergalactic space more than ten billion years ago. Collect enough of these ancient glimmers and you get a snapshot of the primordial cosmos, a rough picture of the first galaxies that formed after the Big Bang. Thanks to sky-mapping projects like the Sloan Digital Sky Survey, we also know quite a bit about the structure of the current universe. We know that it has expanded into a vast web of galaxies, strung together in clumps and filaments, with gigantic voids in between.

How do you follow a galaxy through nearly all of time? You build a new universe.
The real challenge for cosmology is figuring out exactly what happened to those first nascent galaxies. Our telescopes don't let us watch them in time-lapse; we can't fast forward our images of the young universe. Instead, cosmologists must craft mathematical narratives that explain why some of those galaxies flew apart from one another, while others merged and fell into the enormous clusters and filaments that we see around us today. Even when cosmologists manage to cobble together a plausible such story, they find it difficult to check their work. If you can't see a galaxy at every stage of its evolution, how do you make sure your story about it matches up with reality? How do you follow a galaxy through nearly all of time? Thanks to the astonishing computational power of supercomputers, a solution to this problem is beginning to emerge: You build a new universe.

In October, the world's third fastest supercomputer, Mira, is scheduled to run the largest, most complex universe simulation ever attempted. The simulation will cram more than 12 billion years worth of cosmic evolution into just two weeks, tracking trillions of particles as they slowly coalesce into the web-like structure that defines our universe on a large scale. Cosmic simulations have been around for decades, but the technology needed to run a trillion-particle simulation only recently became available. Thanks to Moore's Law, that technology is getting better every year. If Moore's Law holds, the supercomputers of the late 2010s will be a thousand times more powerful than Mira and her peers. That means computational cosmologists will be able to run more simulations at faster speeds and higher resolutions. The virtual universes they create will become the testing ground for our most sophisticated ideas about the cosmos.

Salman Habib is a senior physicist at the Argonne National Laboratory and the leader of the research team working with Mira to create simulations of the universe. Last week, I talked to Habib about cosmology, supercomputing, and what Mira might tell us about the enormous cosmic web we find ourselves in.

Help me get a handle on how your project is going to work. As I understand it, you're going to create a computer simulation of the early universe just after the Big Bang, and in this simulation you will have trillions of virtual particles interacting with each other -- and with the laws of physics -- over a time period of more than 13 billion years. And once the simulation has run its course, you'll be looking to see if what comes out at the end resembles what we see with our telescopes. Is that right?

Habib: That's a good approximation of it. Our primary interest is large-scale structure formation throughout the universe and so we try to begin our simulations well after the Big Bang, and even well after the microwave background era. Let me explain why. We're not sure how to simulate the very beginning of the universe because the physics are very complicated and partially unknown, and even if we could, the early universe is structurally homogenous relative to the complexity that we see now, so you don't need a supercomputer to simulate it. Later on, at the time of the microwave background radiation, we have a much better idea about what's going on. WMAP and Planck have given us a really clear picture of what the universe looked like at that time, but even then the universe is still very homogenous -- its density perturbations are something like one part in a hundred thousand. With that kind of homogeneity, you can still do the calculations and modeling without a supercomputer. But if you fast forward to the point where the universe is about a million times denser than it is now, that's when things get so complicated that you want to hand over the calculations to a supercomputer.

Now the trillions of particles we're talking about aren't supposed to be actual physical particles like protons or neutrons or whatever. Because these trillions of particles are meant to represent the entire universe, they are extremely massive, something in the range of a billion suns. We know the gravitational mechanics of how these particles interact, and so we evolve them forward to see what kind of densities and structure they produce, both as a result of gravity and the expansion of the universe. So, that's essentially what the simulation does: it takes an initial condition and moves it forward to the present to see if our ideas about structure formation in the universe are correct.

At the largest scales, how would you describe the structure of the universe as we see it today through our telescopes? Some say it's web-like or that it's composed of sheets of filaments -- are those accurate descriptions?

Habib: That's a very accurate way to think about it. People often conceive of it as a cosmic web, a picture that dates back to the Soviet physicist Yakov Zel'dovich who had this very deep insight about how structure forms in the universe. The idea is that initially the universe is very smooth, very homogenous, with few perturbations. If you looked at it, you wouldn't see much. But then as the universe expands, gravity causes matter to attract and to form local structures. The first structures to form are sheets, and where the sheets intersect you get filaments, and where the filaments intersect you get clumps. As time progresses, you can start to see the basic structure where you have this enormous web of voids, filaments and clumps. The sheets are very thin, very ephemeral, so it is much harder to see them, but the rest of the structure is very sharp and clear, especially as seen by the Sloan Digital Sky Survey.

Have previous simulations been successful in producing the structure we see with telescopes?

Habib: Oh yes, the web-like structure is completely borne out by simulations. Simulations date back a long way; one of the earliest -- the one I consider to be the precursor to modern simulations -- was done in the late 1960s by the Canadian-American cosmologist Jim Peebles. He spent a summer at Los Alamos and while he was there he was able to perform a 300-particle simulation, which is of course quite small compared to today's simulations. People have been running larger and larger simulations since then, and when they do, they consistently see this same web-like structure.

Is there an aesthetic component to these simulations? Can you actually see galaxies forming?

Habib: There is definitely an aesthetic component. We're looking at an actual image of the structure, but you can't see galaxies forming. It's not quite that granular, and besides these are gravity-only simulations. For large-scale structure simulations, gravity is all you need to understand how you get sheets and filaments and clumps. If you want to see how galaxies form, you need the rest of physics -- you need individual atoms, angular momentum, gas physics, etc. These are enormously complicated processes and we don't yet have the computing power to run them on the scale of the entire universe. There are people who do simulate galaxy formation with supercomputers, but they have to do it over much smaller volumes of the universe.

Some of the inflationary models for the early Universe suggest a process that would continue to produce additional universes, perhaps with their own laws of physics. Certainly that's not something we could model with a computer now, but might it be someday?

Habib: It could be, but we'd have to understand the theory better. The theory you're talking about, eternal inflation, has two issues. First, the sheer difficulty of the calculations, but second the theory itself is not well defined yet. I would argue that, at the moment, theories like eternal inflation are in the realm of speculative physics. There are models for eternal inflation -- I've written papers about them, and so have a lot of other people -- but if you go and look at the equations, they are not very well defined. That's because when you talk about producing new universes, you're talking about the intersection between quantum mechanics and gravity, and we don't yet have a satisfactory theory of quantum gravity. We have candidates for what might someday morph into an satisfactory theory, but we can't say for sure. The multiverse idea is interesting and provocative, but it's a work in progress.

What happens when you let the models run past the present? Time-wise, what's the farthest that someone has taken one of these simulations?

Habib: That's an interesting question. We usually just stop the simulations at the present, because we're still trying to understand how we got here, but there's no particular reason to stop them. You can continue to run them forward and some people have done that in the past. What they've found is that if you run the universe far enough into the future it expands into a pretty bleak place.

"If you run the universe far enough into the future it expands into a pretty bleak place."
All the matter runs away from each other, because space is being created at an ever-accelerating rate. In fact, people often joke that this is the right time to do cosmology because trillions of years from now we won't be able to see anything: Everything will have receded out of sight. So yes, we can run these simulations into the future, but it's not that interesting. The universe is much more interesting now than it's going to be in the future, provided that this accelerating expansion phase of the universe continues as we expect it to.

Your project was made possible by the development of the Mira supercomputer, the third-fastest computer in the world. Can you describe what makes Mira so special?

Habib: Let me say one or two things about supercomputers. Every few years supercomputers become about 10 times more powerful, so with each new generation you get quite a leap in capabilities. Not only do supercomputers get faster, but they get much larger, which allows you to run much bigger problems. What distinguishes a supercomputer like Mira from a normal computer is that it has a very large number of computational units. A simplified way to think about it is to imagine having a million laptops that you've networked in such a way that they're able to communicate with each other very quickly. Now you split your problem up into a million chunks and you give each chunk to a laptop, and the laptop works on its chunk and passes the data around as needed, and eventually your problem gets solved.

What makes all of these simulations possible is the sheer size of the supercomputers. For example, the Mira has close to a petabyte of memory. If you tried to do a simulation like this on a normal computer, you wouldn't be able to fit it, and even if you could fit it, if you tried to run it, it would never finish. With Mira, we're able to complete these universe simulations in the span of a week or two.

I know that supercomputers like Mira are used for all kinds of scientific experiments outside of cosmology. What else will it be used for in the next few years?

Habib: There are a large number of applications. People use supercomputers to determine the properties of materials, to understand combustion, to figure out how a flame works. They're also used to determine fluid dynamics; for instance you might want to know how air flows around the wing of an aircraft, and you can calculate that quite precisely with a supercomputer. In astrophysics there are all sorts of applications; people use supercomputers to study intergalactic gas, the formation of stars, supernovae and so on.

Moore's Law tells us that processing power increases exponentially. Assuming the next few years bring a huge leap in processing power, would you rather use it to perform these experiments quicker, or at a higher complexity?

Habib: There's a difficulty that we're running up against with Moore's Law. If you want to get more performance out of these computers, you can do it two ways: You can make the computational units switch faster or you can add more computational units. It turns out that if you want to make the units switch faster, you need more power. We've reached a limit where we can, in principle, build a faster machine, but it would cost us many gigawatts of power to actually run it and we simply can't afford to do that. So conventional Moore's Law is already reaching a breaking point because of this power barrier.

Now if you want to solve this problem by reducing the amount of power used by the switches in the computer, then you have to reduce the voltage, but if you reduce the voltage you get more errors. So the next generation of computers -- in five years or so -- promises to be very different. We may have to program them in different ways, and we may have to think about how to power them differently, or how to correct for errors. It's going to be interesting and in some senses it's going to be more painful than it is now.

Now around 2018 or 2020, somewhere around that time scale, these machines are supposed to become a thousand times faster than they are right now. There are a lot of studies being done to figure out what you could do with a machine like that, but whether we'll actually get there, I don't know. It's not yet clear that there will be investment in the technologies we need to get us there. There is some hope that there will be investment, because supercomputer simulations are increasingly being used outside the basic sciences. Supercomputers are playing a big role in the development of new technologies. For instance, you can design a diesel engine without ever building a prototype simply by simulating it with a supercomputer.

It seems like a large, sped up version of one of these universe simulations would be perfect as a piece of public art. Has anyone tried anything like that?

Habib: That's an interesting thought. The question is how you would actually show it, because it is a dynamic object. You could have it as a projection like you see at planetariums and that would be very beautiful, but really you have to see it in three dimensions. Until you see it in three dimensions you cannot appreciate how beautiful the structure is. What would be neat is a large-scale hologram -- something where you could actually see the structure pop up around you. That would really be something to see.

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by Steve Koppes, The University of Chicago News Office

Kavli Institute directs national collaboration on deepest questions of dark energy, dark matter, and cosmic inflation

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Sometimes a scientist can only laugh in the face of a seemingly insurmountable challenge.

Such is the case with cracking the mystery of dark energy and its repulsive gravity, which is causing the expansion of the universe to accelerate.

"People don't even get the term 'repulsive gravity' because the defining feature of gravity is that it's attractive," says Michael Turner, director of the Kavli Institute for Cosmological Physics. "What do you mean, repulsive gravity? Do you mean the theory is repulsive?" he jokes.

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The time is ripe to solve the dark matter problem. Our Physics Frontiers Center hopes to shed critical light on dark matter."
-Rocky Kolb
Professor

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Turner calls dark energy "the most profound mystery in all of science." Cracking the problem requires collaborations of original thinkers working beyond the limits of current theories. That's why dark energy is one of three cosmological puzzles that the Kavli Institute is tackling with a five-year, $17 million Physics Frontiers Center grant from the National Science Foundation.

Also high on the institute's research agenda are the riddles of dark matter and cosmic inflation. Along with dark energy, these are the three pillars of modern cosmological theory, "and none of them can be explained with physics that we know," Turner says. "They're all pointing to new physics."

Transforming cosmology
During its first decade as a Physics Frontier Center, the Kavli Institute helped to establish the current cosmological paradigm. Originally called the Center for Cosmological Physics, the Institute was founded in 2001 with a $15 million NSF grant. The Institute is launching its second decade with 21 key collaborators around the country and 15 institutional partners, including Argonne National Laboratory and Fermi National Accelerator Laboratory.

The NSF created the Physics Frontiers Centers program to make significant advances at some of the most important intellectual frontiers in diverse physics subfields, says Joseph Dehmer, director of NSF's division of physics.

"By all measures, this has happened, and the 10 PFCs now operating reflect the extremely high standards of scholarship and synergy hoped for," Dehmer says. "An unexpected and most welcome benefit is that the PFCs act as talent magnets, drawing high levels of talent into physics. Another not unexpected benefit is that the triennial PFC competition constitutes a serious, high-level discussion across the subfields of physics - a rare 'unity of physics' event in an increasingly specialized field."

Argonne is a new partner in the UChicago PFC. Argonne and Kavli Institute scientists will develop large-scale cosmological simulations on the laboratory's supercomputers, as well as sensitive new detectors for the South Pole Telescope, which studies the cosmic microwave background radiation leftover from the birth of the universe. Kavli Institute scientists will investigate the dark energy question with the SPT and the Dark Energy Survey. The latter project, led by Fermilab, will collect data on approximately 300 million galaxies spanning two-thirds the history of the universe in order to measure dark energy with new precision.

New form of matter?
The mystery of dark matter may be easier to solve. Kavli Institute scientists hope to accomplish this feat within the next decade. They suspect that dark matter is made of a new form of matter, something that does not consist of quarks, neutrons or protons.

Dark matter may reveal itself through any or all of three means: direct detection via ground-based detectors at the Chicagoland Observatory for Underground Particle Physics (COUPP), indirect detection in the galaxy halo via satellites, and production of the particles at the Large Hadron Collider at CERN, the European particle physics laboratory.

"Right now, there is confusion - claims of possible detections, counter-claims, and spirited debate - and the time is ripe to solve the dark matter problem. Our PFC hopes to shed critical light on dark matter," says Rocky Kolb, the University's Arthur Holly Compton Distinguished Service Professor in Astronomy & Astrophysics, who leads the PFC's dark matter effort.

Cosmic inflation is a different kind of problem. It has emerged as the most important cosmological concept since the Big Bang theory, but many of its claims have not yet been thoroughly tested. Inflation proposes that the universe expanded extremely rapidly in a tiny fraction of a second after the Big Bang. Such a swift expansion would explain some important questions that Big Bang theory alone has been unable to answer.

"We have some circumstantial evidence that inflation took place, but we'd like to make the case very strongly," says John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics. A more direct indication of inflation would be to look for a minute sign of polarization in the cosmic microwave background, the afterglow of the Big Bang.

For the last decade, center scientists, including Carlstrom and the late Bruce Winstein, have been developing a technology capable of measuring this polarization. Now they need to deploy that technology to see what they can find.

The successful Kavli Institute proposal for the Physics Frontiers Center was more than two years in the making and included significant support from the University administration and behind-the-scenes personnel.

Winstein, the Samuel K. Allison Distinguished Service Professor in Physics and founder of the original PFC, also played a big role in developing the proposal for renewed funding. Winstein, who lost a four-year battle with cancer in Feb. 2011, worked on the proposal until his last days, Turner says.

"During the last months of his life, he was parceling out his time only to the most important things, and we got a lot of his time. Our PFC is part of Bruce's legacy."

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KICP Members: John E. Carlstrom; Edward W. Kolb; Michael S. Turner; Bruce D. Winstein

The University of Chicago News Office

Eight billion years ago, rays of light from distant galaxies began their long journey to Earth. That ancient starlight has now found its way to a mountaintop in Chile, where the newly constructed Dark Energy Camera, the most powerful sky-mapping machine ever created, has captured and recorded it for the first time.

That light may hold within it the answer to one of the biggest mysteries in physics: Why the expansion of the universe is speeding up.

Scientists in the international Dark Energy Survey collaboration, which includes the University of Chicago's Kavli Institute for Cosmological Physics, announced this week that the Dark Energy Camera, the product of eight years of planning and construction by scientists, engineers, and technicians on three continents, has achieved first light. The first pictures of the southern sky were taken by the 570-megapixel camera on Sept. 12.

"The achievement of first light through the Dark Energy Camera begins a significant new era in our exploration of the cosmic frontier," said James Siegrist, associate director of science for high-energy physics with the U.S. Department of Energy. "The results of this survey will bring us closer to understanding the mystery of dark energy, and what it means for the universe."

The Dark Energy Camera was constructed at the U.S. Department of Energy's Fermi National Accelerator Laboratory, and mounted on the Victor M. Blanco telescope at the National Science Foundation's Cerro Tololo Inter-American Observatory in Chile, which is the southern branch of the U.S. National Optical Astronomy Observatory. With this device, roughly the size of a phone booth, astronomers and physicists will probe the mystery of dark energy - the force they believe is causing the universe to expand faster and faster.

"The Dark Energy Survey will help us understand why the expansion of the universe is accelerating, rather than slowing due to gravity," said Brenna Flaugher, project manager and scientist at Fermilab. "It is extremely satisfying to see the efforts of all the people involved in this project finally come together."

The Dark Energy Camera is the most powerful survey instrument of its kind, able to see light from over 100,000 galaxies up to 8 billion light years away in each snapshot. The camera's array of 62 charged-coupled devices has an unprecedented sensitivity to very red light, and along with the Blanco telescope’s large light-gathering mirror (which spans 13 feet across), will allow scientists from around the world to pursue investigations ranging from studies of asteroids in our own solar system to the understanding of the origins and the fate of the universe.

"We're very excited to bring the Dark Energy Camera online and make it available for the astronomical community through NOAO's open access telescope allocation," said Chris Smith, director of the Cerro-Tololo Inter-American Observatory. "With it, we provide astronomers from all over the world a powerful new tool to explore the outstanding questions of our time, perhaps the most pressing of which is the nature of dark energy."

Scientists in the Dark Energy Survey collaboration will use the new camera to carry out the largest galaxy survey ever undertaken, and will use that data to carry out four probes of dark energy, studying galaxy clusters, supernovae, the large-scale clumping of galaxies and weak gravitational lensing. This will be the first time all four of these methods will be possible in a single experiment.

The Dark Energy Survey is expected to begin in December, after the camera is fully tested, and will take advantage of the excellent atmospheric conditions in the Chilean Andes to deliver pictures with the sharpest resolution seen in such a wide-field astronomy survey. In just its first few nights of testing, the camera has already delivered images with excellent and nearly uniform spatial resolution.

Over five years, the survey will create detailed color images of one-eighth of the sky, or 5,000 square degrees, to discover and measure 300 million galaxies, 100,000 galaxy clusters and 4,000 supernovae.

The Dark Energy Survey is supported by funding from the U.S. Department of Energy; the National Science Foundation; funding agencies in the United Kingdom, Spain, Brazil, Germany and Switzerland; and the participating DES institutions.

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Released by Fermilab and the National Optical Astronomy Observatory on behalf of the Dark Energy Survey collaboration. NOAO is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.

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Related Links:
KICP Members: Joshua A. Frieman
Scientific projects: Dark Energy Survey (DES)

Discovery Channel's "Daily Planet"

Discovery Channel's "Daily Planet" show visits the COUPP-4kg dark matter search at SNOLAB. COUPP-4kg is presently taking data in this underground laboratory, while the installation of the COUPP-60kg chamber proceeds. Eric Dahl, a former KICP Fellow and now faculty at Northwestern University, guides the tour. The collaboration is presently designing a larger and final chamber, COUPP-500kg.

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KICP Members: Juan I. Collar; Eric Dahl; Russell Neilson
KICP Students: Drew Fustin; Alan Robinson
Scientific projects: Chicagoland Observatory for Underground Particle Physics (COUPP)

Fermilab Press Room

Eight billion years ago, rays of light from distant galaxies began their long journey to Earth. That ancient starlight has now found its way to a mountaintop in Chile, where the newly-constructed Dark Energy Camera, the most powerful sky-mapping machine ever created, has captured and recorded it for the first time.

That light may hold within it the answer to one of the biggest mysteries in physics - why the expansion of the universe is speeding up.

Scientists in the international Dark Energy Survey collaboration announced this week that the Dark Energy Camera, the product of eight years of planning and construction by scientists, engineers, and technicians on three continents, has achieved first light. The first pictures of the southern sky were taken by the 570-megapixel camera on Sept. 12.

"The achievement of first light through the Dark Energy Camera begins a significant new era in our exploration of the cosmic frontier," said James Siegrist, associate director of science for high energy physics with the U.S. Department of Energy. "The results of this survey will bring us closer to understanding the mystery of dark energy, and what it means for the universe."

The Dark Energy Camera was constructed at the U.S. Department of Energy's (DOE) Fermi National Accelerator Laboratory in Batavia, Illinois, and mounted on the Victor M. Blanco telescope at the National Science Foundation's Cerro Tololo Inter-American Observatory (CTIO) in Chile, which is the southern branch of the U.S. National Optical Astronomy Observatory (NOAO). With this device, roughly the size of a phone booth, astronomers and physicists will probe the mystery of dark energy, the force they believe is causing the universe to expand faster and faster.

"The Dark Energy Survey will help us understand why the expansion of the universe is accelerating, rather than slowing due to gravity," said Brenna Flaugher, project manager and scientist at Fermilab. "It is extremely satisfying to see the efforts of all the people involved in this project finally come together."

The Dark Energy Camera is the most powerful survey instrument of its kind, able to see light from over 100,000 galaxies up to 8 billion light years away in each snapshot. The camera’s array of 62 charged-coupled devices has an unprecedented sensitivity to very red light, and along with the Blanco telescope's large light-gathering mirror (which spans 13 feet across), will allow scientists from around the world to pursue investigations ranging from studies of asteroids in our own Solar System to the understanding of the origins and the fate of the universe.

"We're very excited to bring the Dark Energy Camera online and make it available for the astronomical community through NOAO's open access telescope allocation," said Chris Smith, director of the Cerro-Tololo Inter-American Observatory. "With it, we provide astronomers from all over the world a powerful new tool to explore the outstanding questions of our time, perhaps the most pressing of which is the nature of dark energy."

Scientists in the Dark Energy Survey collaboration will use the new camera to carry out the largest galaxy survey ever undertaken, and will use that data to carry out four probes of dark energy, studying galaxy clusters, supernovae, the large-scale clumping of galaxies and weak gravitational lensing. This will be the first time all four of these methods will be possible in a single experiment.

The Dark Energy Survey is expected to begin in December, after the camera is fully tested, and will take advantage of the excellent atmospheric conditions in the Chilean Andes to deliver pictures with the sharpest resolution seen in such a wide-field astronomy survey. In just its first few nights of testing, the camera has already delivered images with excellent and nearly uniform spatial resolution.

Over five years, the survey will create detailed color images of one-eighth of the sky, or 5,000 square degrees, to discover and measure 300 million galaxies, 100,000 galaxy clusters and 4,000 supernovae.

The Dark Energy Survey is supported by funding from the U.S. Department of Energy; the National Science Foundation; funding agencies in the United Kingdom, Spain, Brazil, Germany and Switzerland; and the participating DES institutions.

More information about the Dark Energy Survey, including the list of participating institutions, is available at the project website: www.darkenergysurvey.org.

For a summary of the major components contributed to the Dark Energy Camera by the participating institutions, read these symmetry articles: www.symmetrymagazine.org/cms/?pid=1000880, http://www.symmetrymagazine.org/article/september-2012/the-dark-energy-camera-opens-its-eyes

Released by Fermilab and the National Optical Astronomy Observatory (NOAO) on behalf of the Dark Energy Survey collaboration. NOAO is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under cooperative agreement with the National Science Foundation.

Fermilab is America's premier national laboratory for particle physics research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance, LLC. Visit Fermilab's website at www.fnal.gov.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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Scientific projects: Dark Energy Survey (DES)

by Clara Moskowitz, SPACE.com

Scientists would love to be able to rewind the universe and watch what happened from the start. Since that's not possible, researchers must create their own mini-universes inside computers and unleash the laws of physics on them, to study their evolution.

Now researchers are planning the most detailed, largest-scale simulation of this kind to date. One of the main mysteries they hope to solve with it is the origin of the dark energy that's causing the universe to accelerate in its expansion.

The new simulation is a project led by physicists Salman Habib and Katrin Heitmann of Illinois' Argonne National Laboratory, and will run on the lab's Mira supercomputer, the third-fastest computer in the world, starting in the next month or two. The program will use trillions of "particles" - elements in the simulation that stand in for small bits of matter. The computer will let time run, and watch as the particles move through space in response to the forces acting on them.

As the simulation progresses, these bits of matter will clump together under gravity to form larger and larger blobs representing galaxies, galaxy clusters and superclusters. To evolve the universe from the Big Bang 13.7 billion years forward to today, the simulation will take up to two weeks.

Testing the theory
The ultimate goal is to compare the best telescope observations of structure in the universe to the structure displayed in the computer model, to test the reigning theory of cosmology.

"We are trying to look for subtle ways in which it's wrong," Habib told SPACE.com. "That's why you need these very high-resolution, very large-scale simulations to see if the observations don't match the predictions."

Dark energy is the name given to whatever is causing the expansion of the universe to accelerate. When this acceleration was first discovered in the 1990s, it shocked the science community, because theories predicted the universe's expansion would be steady or slowing down, because of the inward pull of gravity.

The current reigning theory posits that dark energy is what's called the cosmological constant, a term Einstein first thought to put into his equations of general relativity to represent the vacuum energy of the universe. Although Einstein ultimately decided not to include the term, scientists later realized that it could explain the current observations of the expansion of the universe.

However, cosmologists aren't satisfied with this explanation, Habib said.

Another possibility
"It's just a single number entered as an extra term in the equations," he said. "The problem is that if you ask what its value should be, it's enormous - many orders of magnitude bigger than what is actually observed."

While simulations based on the cosmological constant so far appear to match what's seen in large-scale observations of the universe, scientists think that next-generation observations may reveal discrepant details.

If a cosmological constant is not to blame for the accelerated expansion of the universe, another possibility is that space contains some other type of mass or energy, such as a field, that is pulling everything apart.

"It's basically guesswork; it could be like this, or it could be like that," Habib said. "Either way it's very interesting."

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by Steve Koppes, The University of Chicago News Office

Analysis of data from the National Science Foundation's South Pole Telescope, for the first time, more precisely defines the period of cosmological evolution when the first stars and galaxies formed and gradually illuminated the universe. The data indicate that this period, called the epoch of reionization, was shorter than theorists speculated - and that it ended early.

"We find that the epoch of reionization lasted less than 500 million years and began when the universe was at least 250 million years old," said Oliver Zahn, a postdoctoral fellow at the Berkeley Center for Cosmological Physics at the University of California, Berkeley, who led the study. "Before this measurement, scientists believed that reionization lasted 750 million years or longer, and had no evidence as to when reionization began."

The findings by Zahn, his colleagues at UChicago's Kavli Institute for Cosmological Physics and elsewhere have been published in a pair of papers appearing in the Sept. 1, 2012 issue of the Astrophysical Journal. Their latest results are based on a new analysis that combines measurements taken by the South Pole Telescope at three frequencies, and extends these measurements to a larger area covering approximately 2 percent of the sky. The 10-meter South Pole Telescope operates at millimeter wavelengths to make high-resolution images of the cosmic microwave background, the light left over from the big bang.

"Studying the epoch of reionization is important because it represents one of the few ways by which we can study the first stars and galaxies," said study co-author John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics.

Before the first stars formed, most matter in the universe took the form of neutral hydrogen atoms. The radiation from the first stars transformed the neutral gas into an electron-proton plasma. Observations with the Wilkinson Microwave Anisotropy Probe satellite of polarized signals in the CMB indicate that this epoch occurred nearly 13 billion years ago, but these observations give no indication of when the epoch began or how long it lasted.

The first stars that formed were probably 30 to 300 times more massive than the sun and millions of times as bright, burning for only a few million years before exploding. The energetic ultraviolet light from these stars was capable of splitting hydrogen atoms back into electrons and protons, thus ionizing them.

Scientists believe that during reinoization, the first galaxies to form ionized "bubbles" in the neutral gas surrounding them. Electrons in these bubbles would scatter with light particles from the cosmic microwave background. This would create small hot and cold spots in the CMB depending on whether a bubble is moving toward or away from Earth. A longer epoch of reionization would create more bubbles, leading to a larger signal in the CMB.

The epoch's short duration indicates that reionization was more explosive than scientists had previously thought. It suggests that massive galaxies played a key role in reionization, because smaller galaxies would have formed much earlier. Rapid reionization also argues against many proposed astrophysical phenomena that would slow the process.

This is only the beginning of what astronomers expect to learn about reionization from the South Pole Telescope. The current results are based on only the first third of the telescope's full survey. Additional work is under way to combine South Pole Telescope maps with ones made by the Herschel satellite to further increase sensitivity to the reionization signal.

"We expect to measure the duration of reionization to within 50 million years with the current survey," said study co-author Christian Reichardt, a Berkeley astrophysicist. "With planned upgrades to the instrument, we hope to improve this even further in the next five years."

The 280-ton South Pole Telescope stands 75 feet tall and is the largest astronomical telescope ever built in Antarctica's clear, dry air. Sited at the National Science Foundation's Amundsen-Scott South Pole station at the geographic South Pole, it stands at an elevation of 9,300 feet on the polar plateau. Because of its location at the Earth's axis, it can conduct long-term observations of a single patch of sky.

UChicago leads the South Pole Telescope collaboration, which includes research groups from Argonne National Laboratory, Cardiff University, Case Western Reserve University, Harvard University, Ludwig-Maximilians-Universitat, Smithsonian Astrophysical Observatory, McGill University, University of California at Berkeley, University of California at Davis, University of Colorado at Boulder, University of Michigan and individual scientists at several other institutions.

The South Pole Telescope is primarily funded by the NSF's Office of Polar Programs. Partial support also is provided by the NSF-funded Physics Frontier Center of UChicago's Kavli Institute for Cosmological Physics, the Kavli Foundation, and the Gordon and Betty Moore Foundation.

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Scientific projects: South Pole Telescope (SPT)

by Steve Koppes, The University of Chicago News Office

The University of Chicago's Stephan Meyer, professor in astronomy & astrophysics and the Kavli Institute for Cosmological Physics, has received a share of his second Gruber Cosmology Prize for his work as a member of the Wilkinson Microwave Anisotropy Probe.

This year's $500,000 Gruber Cosmology Prize went to John Hopkins University's Charles L. Bennett, who heads the 26-member WMAP collaboration, and his associates for building the WMAP satellite to make "observations of the so-called 'echo of the Big Bang,' the Cosmic Microwave Background radiation, to determine the universe’s vital statistics - its age, content, geometry and origin." The prize citation further noted that, "This feat in turn has helped transform cosmology itself into a precision science."

NASA launched the WMAP satellite in 2001 to make precision measurements of the Microwave Background anisotropy, or structure. WMAP is named for the late David Wilkinson, who was Meyer's PhD advisor at Princeton University. In 1994 Wilkinson served as a distinguished visiting professor at UChicago's Enrico Fermi Institute, where he worked on the early ideas for the WMAP instrumentation.

Meyer previously had received a share of the 2006 Gruber Cosmology Prize with fellow members of the Cosmic Background Explorer collaboration.

NASA launched the COBE satellite in 1989 to precisely map the cosmic microwave background radiation. In 1992, the COBE team confirmed that the universe was born in a hot big bang. Two members of the COBE team, John Mather of NASA's Goddard Space Flight Center, and George Smoot of the University of California, Berkeley, also received the 2006 Nobel Prize in physics for this work.

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Scientific projects: Wilkinson Microwave Anisotropy Probe (WMAP)

Kavli Foundation News

On the eve of their NASA press conference, Michael McDonald, Kavli Institute for Astrophysics and Space Research at MIT, and Bradford Benson, Kavli Institute for Cosmological Physics, University of Chicago, discuss the discovery of the Phoenix Cluster -- a galaxy cluster for the record books.

TODAY, NASA ANNOUNCED that astronomers have found a massive galaxy cluster with astounding and unexpected properties - producing stars at a prodigious rate astronomers have not seen in other galaxy clusters.

The discovery of the Phoenix Cluster, and its central galaxy producing 740 stars per year, is prompting astronomers to re-think how galaxy clusters, among the largest structures in the universe, form and evolve over cosmic time. No nearby galaxy clusters (and therefore closer in cosmic time) produce stars in their central galaxies at such a high rate. The vigorous starburst in Phoenix is not thought to be sustainable for more than a few hundred million years because anything exceeding that would make the central galaxy in the cluster larger than anything else seen in the universe.

On the eve of the NASA announcement, Hubble Fellow Michael McDonald, a researcher at the Kavli Institute for Astrophysics and Space Research at MIT and also the lead author of a paper appearing Aug. 16 in the journal Nature, and Bradford Benson, a researcher at the Kavli Institute for Cosmological Physics at the University of Chicago and a co-author of the paper in Nature, spoke with The Kavli Foundation about the discovery.

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THE KAVLI FOUNDATION (TKF): Let's start with the basics. How large is the Phoenix Cluster, where is it and how old is it?

MICHAEL MCDONALD: It's one of the most massive clusters in the universe, maybe in the top two or three - and perhaps it is the largest that we know of in the universe. It's 5.7 billion light-years away, so we're seeing it as it looked 5.7 billion years ago.

TKF: So it's much older now than it was at the time we are observing it.

MCDONALD: That's right.

BENSON: It would also be more massive now, because the central galaxy in a cluster grows through mergers over time, and clusters themselves merge with other clusters and grow bigger. But even when we’re observing it, at 5.7 billion years ago, it’s already one of the most massive clusters in the universe that we know about - even today.

TKF: How did you become interested in this particular cluster, and did you know immediately that it was special and worth exploring?

BENSON: Originally this cluster was discovered by the South Pole Telescope (SPT), which is a ten-meter telescope that studies millimeter wavelength light from these objects. SPT finds clusters of galaxies in a really unique way. It detects them indirectly, by detecting the shadows these clusters make in the cosmic microwave background, which is the light that's left over from the Big Bang. Clusters of galaxies are one of the few things in the universe that are so massive, they're able to create shadows in the cosmic microwave background. Effectively, the light from the Big Bang travels 14 billion years across the entire observable universe, and these clusters of galaxies make shadows in that light. It turns out this is a very effective way to find the most massive distant clusters in the universe. The Phoenix Cluster was discovered as part of a survey by the South Pole Telescope that observed 2500 square degrees of the sky, or about 15-percent of the total sky.

TKF: At what point did the scientific community know this particular cluster was different from most others observed?

BENSON: After we detected the Phoenix Cluster, we followed it up to measure its redshift -- in other words to determine its distance -- and also made several other measurements in optical, X-ray, infrared, ultraviolet and other wavelengths to learn about the properties of gas and stars in the cluster.

Mike and I were particularly interested in X-ray observations. This same hot gas that scatters a small percentage of CMB photons as they pass through the cluster also emits X-rays very brightly. The gas is on the order of 100 million degrees Kelvin, which is hotter then the interior of the Sun. So these are very bright X-ray sources on the sky. The Chandra X-ray telescope was one of the first things we used to follow up this cluster. The Phoenix Cluster stood out as having very high X-ray emission from its center, so much that it made the entire cluster the most luminous X-ray cluster ever observed.

That immediately peaked our interest, because it suggested that cool gas was condensing in the center of the cluster. So we began to get as much data as we could to try to understand what else was happening in this cluster – in particular the star formation and the central black hole. And that's where Mike came in; he was instrumental in accumulating a lot of that extra data, to figure out how this hot gas is turning into stars.

TKF: What first hints did you have that the rate of star formation was so high in Phoenix?

MCDONALD: As Brad said, when we first got these X-ray measurements from Chandra, it was pretty obvious this was a unique cluster. Specifically, the center of the cluster was very dense and cooling very rapidly. This is a process I've studied in other galaxy clusters, so I thought immediately that there must be vigorous star formation if we see all this cooling. I started putting together some of the data that we already had, as well as data from observatory archives and new data from both space- and ground-based telescopes. With all this data in hand, we saw that the central galaxy was very blue, indicating it was forming a lot of young stars.

TKF: And that was a surprise for a cluster so far away, correct?

MCDONALD: Right. There are a significant number of nearby clusters that are what we call "cool core", or "cooling flow" clusters. There's been some evidence that this strong cooling is a recent phenomenon, and that it did not happen in the early universe. So this is one of the few - or one of the only - clusters that we know of at a high redshift in the early universe that is cooling very rapidly like this.

"The goal is to study more clusters to better understand their evolution. ...We need to compare other clusters to Phoenix - clusters of all ages - to see how they evolve over cosmic time and where the Phoenix Cluster fits into this evolutionary picture." - Bradford Benson

TKF: Why do we think that this didn't happen in the early universe with the same frequency that it does today?

MCDONALD: We don't know for sure that it did not happen in the early universe. It could be that previous surveys just had trouble finding these clusters. So for example a cluster like Phoenix may be hard to detect at X-ray wavelengths initially, because the energy is so concentrated at its center that it could look like a point source - like a quasar, for example. (Quasars are the energetic cores of distant galaxies that surround a central supermassive black hole and appear as point sources of light, as opposed to the energized gas falling into the core of a galaxy cluster)

So you can misidentify extreme clusters as something else, unless you have proof that it's a cluster by indirectly detecting its presence through these shadows on the CMB, or having optical follow-up. So it could be there are in fact very few of these at high redshifts, at earlier times, or it could be we just haven't been able to find them until now.

TKF: What specific roles did each of you play in this project?

BENSON: Originally, I started on this working with the South Pole Telescope, which was making observations of the cosmic microwave background. The primary goal is to use the cosmic microwave background to find clusters of galaxies in this manner that I talked about, with the shadows. So I started working with SPT by developing and building its microwave camera. My interest was primarily to study galaxy clusters in order to learn about dark energy.

Towards that goal, I’ve helped to identify clusters in the SPT survey, including the Phoenix Cluster, follow them up with observations at X-ray wavelengths to understand better what the gas is doing in the cluster at finer angular resolution, and also to work on determining the cluster's mass with Mike.

MCDONALD: I joined in when the X-ray follow-up really started to get off the ground, which Brad has been leading. My job was to look at these clusters at X-ray wavelengths and try to estimate their masses, which would then get fed into Brad's cosmology work on dark energy.

So I have been looking at all the clusters that the SPT observed in the X-ray, and from time-to-time we’ve seen very interesting ones that are useful for more than just cosmology - for dark energy studies. I'm interested more in the actual physics of these clusters, and understanding how they are evolving between the early universe and now. So, the Phoenix Cluster is particularly interesting to me because I’m really interested in these cool cores, these cooling flow clusters. When we saw this, I started to get excited and began gathering all this data, including data on the star formation rate. So I've worked on the follow-up analysis after the original detection.

TKF: At that point did you know the star formation rate was off the charts in this cluster, and what was the team’s initial reaction? At first did you question the result?

MCDONALD: I am a very glass half-full guy. I immediately thought that it was extremely exciting, and I needed people to reign me in. So right away, as soon as we looked at the first spectrum, it was just booming in oxygen emission, which is an indicator of star formation. Then we looked at the cluster in ultraviolet wavelengths, and it was again exceptionally bright. So it was obvious from every angle right away this was really unique.

However, to go from there to something that can convince the science community required several months of checking results and getting additional data. We studied all the different scenarios that could have been biasing our results. We went through everything very carefully to make sure that we weren't missing anything fundamental, and that we were doing all the corrections we needed to do to finally get a convincing, robust estimate of the rate of star formation. That took some time.

TKF: Brad, what was your initial reaction?

BENSON: When the same measurements kept coming in, and they were very consistent with a very high star formation rate - however we measured it - it was extremely exciting to see. This cluster is extremely unique. It is sort of like "the missing link" in cluster evolution. If you look at galaxy clusters today, they are very inefficient at forming stars; they form far fewer stars than you would expect from simulations. At some point in the history of galaxy clusters, you expect the star formation rate to be much higher than what we see in nearby clusters - at essentially the present time. But we really need evidence of that.

The Phoenix Cluster is the first to show extremely high rates of star formation, consistent with what we've expected. So we are seeing this cluster possibly at a stage where it is transitioning from extremely high levels of star formation to a time when the supermassive black hole at the core of its central galaxy turns on, releases more energy into the gas, and only later suppresses star formation.

TKF: Mike, why was it so important to use several different instruments to study this one cluster?

MCDONALD: I think galaxy clusters are one of the few things in astronomy where you really need this full coverage, from all different wavelengths and energies, to get a sense of what's going on. Especially in this cluster, which is so exotic. So, you can only really understand the supermassive black hole at the core of the central galaxy in the Phoenix Cluster with a combination of radio, X-ray, and optical data. Those three things tell us what type of black hole it is, and how it’s giving off its energy.

Meanwhile, the stars being formed are best observed in the ultraviolet and the infrared. You need the combination to get the bright young stars and the stars that are obscured by dust in the early stages of formation. So you need this UV and infrared combination. For the old stars that already exist there, you need more visible wavelength data. X-ray data also gives you total cluster properties. You see the cooling gas and the hot cluster halo.

So you really need this full range of data to piece everything together, and to get all the evidence of what is going on because there are so many different things at play. That is partially why I am very interested in galaxy clusters. I like to use this full range of detection methods and the different telescopes.

TKF: Is it correct to say that the supermassive black hole at the center of the central galaxy in the Phoenix Cluster - and the time we’re observing it, 5.7 billion years ago - is not yet fully mature yet? In other words, that it's not yet creating the kind of feedback energy that would slow the cooling of gas and suppress the formation of stars?

MCDONALD: I think mature is a good term to use. But it's not that the black hole is giving off too little energy. It is actually one of the most powerful active black holes that we know about in cluster cores. Instead, it's giving off energy in the wrong way. It is giving off gamma rays and X-rays at a very large rate. Typically, these cluster-centric black holes are giving off a lot of radio emissions in the form of jets, which can sort of stir up the gas around galaxy. So it almost seems to be confused about where it is. It's sort of acting like it's in an ordinary spiral galaxy, whereas it is really in the center of a galaxy cluster and should be producing these radio jets. So maybe this is something that is in transition now between a quasar-like object and a radio-loud object.

TKF: And a radio jet emission would be more energetic and be able to slow this gas cooling?

MCDONALD: It would not be necessarily more energetic, but it would be the right kind of energy. It would be giving off energy that could couple to the intra-cluster gas. These radio jets can produce shocks and ripples in the intra-cluster medium that heat the gas up. It's kind of like trying to cook a turkey with a blowtorch. You're going to burn one little part of it but you won't cook the whole turkey very well. Whereas a slow gentle heat over a large area cooks the turkey much better.

TKF: And that "gentle" heating - driven by these radio jets from the central black hole - is what will slow the rate at which the gas cools and flows toward the central galaxy. And the result is a suppressed rate of star formation.

MCDONALD: Right. Exactly. Clusters in the local universe have the right amount of radio emission to offset cooling and so you get this really nice balance between radio jets coming from the central black hole heating up the gas, and the cooling of gas. The result is you don't have enough gas left over to form stars. Whereas in the Phoenix Cluster, there is very little radio emission from the central black hole, so you get this runaway cooling of gas that turns into stars. The gamma ray and x-ray emissions coming from central black hole aren't able to keep the gas hot enough to prevent star formation.

TKF: Let's talk a little about what this discovery means - the big picture. Before you studied the Phoenix Cluster, what was your 30-second description of how the central galaxy in clusters formed stars over cosmic time? And what's your new 30-second description?

MCDONALD: The picture as of a few months ago was that the central galaxies in clusters essentially formed via mergers. So you have thousands of galaxies in a cluster, and some of them are eventually going to merge with the central galaxy and you will slowly build up mass in the central galaxy. And it sort of just feeds off the other members. So that's the picture of how these supermassive galaxies form, just by accretion of smaller galaxies.

At the same time there was always another possibility that cooling should also play a role in the growth of a cluster's central galaxy. You have this reservoir of hot gas in the cluster, that should be able to fuel star formation - if it could cool enough. Computer simulations have suggested that this happens, but this was never really observed. Astronomers saw some star formation in the cores of some clusters, but never anywhere near the rate predicted by computer simulations. So this became known as "the cooling flow problem."

And so astronomers recently ruled out the idea that central galaxies in clusters grow by forming stars from the flow of cooling gas in the cluster toward the center.

The discovery of the Phoenix Cluster and its central galaxy throws a wrench into all this. Now we see a galaxy that appears to be forming a substantial number of its stars through this accretion of cooling material from the intra-cluster medium. Even if this goes on for just 100 million years, which is a cosmic blink of an eye, it's going to double the mass of the galaxy. So it's forming a large fraction of its stars not through mergers but through this accretion of cool gas. It's a channel predicted by simulations and by theory, but it's never really been observed until now. So maybe this is a new mechanism for how these galaxies can get so big.

BENSON: From my perspective, within the SPT collaboration, we are interested in this cluster in a slightly different way. It appears that in the Phoenix Cluster, the supermassive black hole at the core of its central galaxy has not turned on fully, at least not to the point where it has started suppressing star formation.

One of the reasons that we think supermassive black holes might be suppressing star formation in local clusters nearby is because we can see they are releasing energy into space between the cluster's galaxies through jets and explosions started by this central black hole.

So when we see something like this - a more distant galaxy cluster where the central black hole is not suppressing star formation - we need to see if we can find more clusters like it. The big question is, when do the black holes at the center of clusters turn on with the energy needed to suppress star formation - like we see in nearby clusters? The goal is to study more clusters to better understand their evolution, and when the black holes are turning on. We need to compare other clusters to Phoenix - clusters of all ages - to see how they evolve over cosmic time and where the Phoenix Cluster fits into this evolutionary picture.

TKF: Where are you both headed next with your research?

MCDONALD: First, I'll be getting more data on this one cluster, Phoenix. The Hubble Space Telescope will allow us to see where star formation is happening - whether there are filaments of star formation or whether it's more smoothly distributed. We'll also be able to separate the new stars from the older ones that lie closer to the core of the central galaxy.

We'll also hopefully obtain data from the new Atacama Large Millimeter/submillimeter Array in Chile, which will tell us how much cold gas there is. And that will give us an exact estimate of how long the starburst can last. If you know how much fuel you have and you know how quickly you're burning it, you can determine how long you can sustain the star formation.

Separately, we're going to try to find more clusters, either like this or unlike this. The reason is that it's really hard to draw any conclusion based on one galaxy cluster. So while this is exciting, it doesn't necessarily tell us about the overall evolution of galaxies and galaxy clusters.

BENSON: We'll be following up on many more clusters found in the SPT survey with the Chandra X-ray telescope. With that we are trying to assemble a larger statistical sample, to try to understand the percentages of how many clusters have similar properties in terms of these cooling cores, and how many of those exhibit similar signs of heightened star formation. Our goal is to better understand if the Phoenix Cluster is a unique, one-in-a-million thing, or if it's rare simply because it's in the midst of a short-lived period in its overall evolution that was more typical for clusters earlier in their formation.

"This discovery in the Phoenix Cluster suggests a whole new twist to that idea about how massive galaxies at the center of galaxy clusters grow. ...It makes the field more exciting from my perspective. It adds a lot of questions." - Michael McDonald

TKF: What excites you most about this discovery?

BENSON: Cosmology tries to answer some of the biggest questions about the universe, such as "How old is it?" and "How did it evolve?" I originally got involved in this from that perspective. For example, I'm trying to use clusters of galaxies to better understand dark energy, which is responsible for the mysterious force causing the universe to expand at an accelerating rate. At the same time, as you use all these astrophysical tools to try to understand cosmology better, you get more and more interested in the astrophysics, in the actual formation of these galaxies and galaxy clusters over time. We want to understand those things better so we can use them as cosmological tools. But they are also interesting by themselves. Unraveling that aspect of the mystery of how clusters form is also interesting.

MCDONALD: For me, this is exciting because in some ways it is reviving a long-held theory that never quite panned out. It has been thought over the last few years that this type of cooling-induced starburst doesn't happen, that galaxy evolution in clusters is very much based on mergers and the assembly of smaller galaxies to make a bigger galaxy.

This discovery in the Phoenix Cluster suggests a whole new twist to that idea about how massive galaxies at the center of galaxy clusters grow, and it allows for another mechanism for the growth of these galaxies. It opens up a whole new area of research, essentially. It allows us to understand the growth of galaxies via a variety of mechanisms, rather than just assembling from mergers. So it makes the field more exciting from my perspective. It adds a lot of questions, which gives us something new to do.

- August 2012

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Scientific projects: South Pole Telescope (SPT)

NASA

WASHINGTON -- Astronomers have found an extraordinary galaxy cluster - one of the largest objects in the Universe - that is breaking several important cosmic records. Observations of this cluster, known as the Phoenix Cluster, with NASA's Chandra X-ray Observatory, the NSF's South Pole Telescope and eight other world-class observatories, may force astronomers to rethink how these colossal structures, and the galaxies that inhabit them, evolve.

Stars are forming in the Phoenix Cluster at the highest rate ever observed for the middle of a galaxy cluster. The object is also the most powerful producer of X-rays of any known cluster, and among the most massive of clusters. The data also suggest that the rate of hot gas cooling in the central regions of the cluster is the largest ever observed.
This galaxy cluster has been dubbed the "Phoenix Cluster" because it is located in the constellation of the Phoenix, and because of its remarkable properties. The cluster is located about 5.7 billion light years from Earth.

"The mythology of the Phoenix - a bird rising from the dead - is a great way to describe this revived object," said Michael McDonald, a Hubble Fellow at the Massachusetts Institute of Technology and the lead author of a paper appearing in the August 16th issue of the journal Nature. "While galaxies at the center of most clusters may have been dormant for billions of years, the central galaxy in this cluster seems to have come back to life with a new burst of star formation."
Like other galaxy clusters, Phoenix contains a vast reservoir of hot gas - containing more normal matter than all of the galaxies in the cluster combined - that can only be detected with X-ray telescopes like Chandra. The prevailing wisdom had once been that this hot gas should cool over time and sink to the galaxy at the center of the cluster, forming huge numbers of stars.

However, most galaxy clusters have formed very few stars over the last few billion years. Astronomers think that the supermassive black hole in the central galaxy of clusters pumps energy into the system, preventing cooling of gas from causing a burst of star formation.

The famous Perseus Cluster is an example of a black hole bellowing out energy and preventing the gas from cooling to form stars at a high rate. Repeated outbursts from the black hole in the center of Perseus, in the form of powerful jets, created giant cavities and produced sound waves with an incredibly deep B-flat note 57 octaves below middle C.

"We thought that these very deep sounds might be found in galaxy clusters everywhere," said co-author Ryan Foley, a Clay Fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "The Phoenix Cluster is showing us this is not the case - or at least there are times the music stops. Jets from the giant black hole at the center of a cluster are apparently not powerful enough to prevent the cluster gas from cooling."
With its black hole not producing powerful enough jets, the center of the Phoenix Cluster is buzzing with stars that are forming about 20 times faster than in the Perseus cluster. The rate is not the highest seen anywhere in the Universe, but the overall record-holding galaxies, located outside clusters, have rates only about twice as high.

The frenetic pace of star birth and cooling of gas in Phoenix are causing both the galaxy and the black hole to add mass very quickly - an important phase that the researchers predict will be relatively short-lived.

"The galaxy and its black hole are undergoing unsustainable growth," said co-author Bradford Benson, of the University of Chicago. "This growth spurt can't last longer than about a hundred million years, otherwise the galaxy and black hole would become much bigger than their counterparts in the nearby Universe."

Remarkably, the Phoenix Cluster and its central galaxy and supermassive black hole are already among the most massive known objects of their type.

Because of their tremendous size, galaxy clusters are crucial objects for studying cosmology and galaxy evolution and so finding one with such extreme properties like the Phoenix Cluster is important.

"This spectacular star burst is a very significant discovery because it suggests we have to rethink how the massive galaxies in the centers of clusters grow," said Martin Rees of Cambridge University, who was not involved with the study. "The cooling of hot gas might be a much more important source of stars than previously thought."

The Phoenix Cluster was originally detected by the National Science Foundation's South Pole Telescope, and later was observed in optical light by the Gemini Observatory in Chile as well as the Blanco 4-meter and Magellan telescopes, also in Chile. The hot gas and its rate of cooling were estimated from Chandra data. To measure the star formation rate in the Phoenix Cluster, several space-based telescopes were used including NASA's WISE and GALEX, and ESA's Herschel.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

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KICP Members: Bradford A. Benson; John E. Carlstrom; Clarence L. Chang; Thomas M. Crawford; Michael D. Gladders; Fredrick W. High; Stephen Hoover; Ryan Keisler; Adam Mantz; Jared Mehl; Stephan S. Meyer; Tom Plagge; Kathryn K. Schaffer
KICP Students: Lindsey E. Bleem; Abigail T. Crites; Tyler Natoli; Kyle Story
Scientific projects: South Pole Telescope (SPT)

by Steve Koppes, The University of Chicago News Office

Astronomers have found an extraordinary galaxy cluster - one of the largest objects in the universe - that is breaking several important cosmic records. The discovery of this cluster, known as the Phoenix Cluster, made with the National Science Foundation's South Pole Telescope, may force astronomers to rethink how these colossal structures, and the galaxies that inhabit them, evolve.

Follow-up observations made in ultraviolet, optical and infrared wavelengths show that stars are forming in this object at the highest rate ever seen in the middle of a galaxy cluster. The object also is the most powerful producer of X-rays of any known cluster, and among the most massive of clusters. The data also suggest that the rate of hot gas cooling in the central regions of the cluster is the largest ever observed.

Officially known as SPT-CLJ2344-4243, this galaxy cluster has been dubbed the "Phoenix Cluster" because it is located in the constellation of the Phoenix, and because of its remarkable properties. Scientists at the University of Chicago's Kavli Institute for Cosmological Physics and their collaborators initially found the cluster, located about 5.7 billion light years from Earth, using the Sunyaev-Zel'dovich effect, the shadow that the cluster makes in fossil light leftover from the big bang.

Predicted in 1972, the effect was first demonstrated to find previously unknown clusters of galaxies by the South Pole Telescope collaboration in 2009. Observations of the effect have since opened a new window for astronomers to discover the most massive, distant clusters in the universe.

"The mythology of the Phoenix - a bird rising from the dead - is a perfect way to describe this revived object," said Michael McDonald, a Hubble Fellow at the Massachusetts Institute of Technology's Kavli Institute for Astrophysics and Space Research. McDonald is the lead author of a paper appearing in the Aug. 16 issue of the journal Nature, which presents these findings. "While galaxies at the center of most clusters have been dead for billions of years, the central galaxy in this cluster seems to have come back to life," McDonald said.

Stars forming at incredible rates
Like other galaxy clusters, Phoenix holds a vast reservoir of hot gas that contains more normal matter than all of the galaxies in the cluster combined. The emission from this reservoir can only be detected with X-ray telescopes like NASA's Chandra X-ray Observatory. The prevailing wisdom had once been that this hot gas should cool over time and sink to the center of the cluster, forming huge numbers of stars.

However, most galaxy clusters have formed very few stars over the last few billion years. Astronomers think that the supermassive black hole in the central galaxy of clusters pumps energy into the system, preventing cooling of gas from causing a burst of star formation. The famous Perseus Cluster is an example of a black hole bellowing out energy and preventing the gas from cooling to form stars at a high rate.

With its black hole not producing powerful enough jets, the center of the Phoenix Cluster is buzzing with stars that are forming 20 times faster than in the Perseus Cluster. This rate is the highest seen in the center of a galaxy cluster and is comparable to the highest seen anywhere in the universe.

The frenetic pace of star birth and cooling of gas in Phoenix are causing both the galaxy and the black hole to add mass very quickly - an important phase that the researchers predict will be relatively short-lived.

"The galaxy and its black hole are undergoing unsustainable growth," said co-author Bradford Benson, a Kavli Institute Fellow at the University of Chicago. "This growth spurt can't last longer than about a hundred million years, otherwise the galaxy and black hole would become much bigger than their counterparts in the nearby universe."

Searching for additional galaxy clusters
Remarkably, the Phoenix Cluster and its central galaxy and supermassive black hole are already among the most massive known objects of their type. Because of their tremendous size, galaxy clusters are crucial objects for studying cosmology and galaxy evolution and so finding one with such extreme properties like the Phoenix Cluster is important.

"The beauty of the SZ effect for cosmology is that it is as easy to detect a cluster of galaxies in the distant reaches of the observable universe as it is for one nearby," said UChicago's John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics. "The magnitude of the effect depends on the mass of the object and not its distance from Earth."

Galaxy clusters contain enough hot gas to create detectable "shadows" in the light left over from the big bang, which also is known as the cosmic microwave background radiation. This light has literally traveled for 14 billion years across the entire observable universe to get to Earth. If it passes through a massive cluster on its way, then a tiny fraction of the light gets scattered to higher energies - the Sunyaev-Zel'dovich effect.

The South Pole Telescope collaboration has now completed an SZ survey of a large region of the sky finding hundreds of distant, massive galaxy clusters. Further follow-up observations of the clusters at X-ray and other wavelengths may reveal the existence of additional Phoenix-like galaxy clusters.

Also contributing observations of the Phoenix Cluster were the Gemini Observatory and the Blanco 4-meter and Magellan telescopes, all in Chile, while several space-based telescopes were used to measure the cluster's star-formation rate.

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KICP Members: Bradford A. Benson; John E. Carlstrom; Clarence L. Chang; Thomas M. Crawford; Michael D. Gladders; Fredrick W. High; Stephen Hoover; Ryan Keisler; Adam Mantz; Jared Mehl; Stephan S. Meyer; Steve Padin; Tom Plagge; Kathryn K. Schaffer
KICP Students: Lindsey E. Bleem; Abigail T. Crites; Tyler Natoli; Kyle Story
Scientific projects: South Pole Telescope (SPT)

Fermilab

Our galaxy, the Milky Way, is a large spiral galaxy surrounded by dozens of smaller satellite galaxies. Scientists have long theorized that occasionally these satellites will pass through the disk of the Milky Way, perturbing both the satellite and the disk. A team of astronomers from Canada and the United States have discovered what may well be the smoking gun of such an encounter, one that occurred close to our position in the galaxy and relatively recently, at least in the cosmological sense.

"We have found evidence that our Milky Way had an encounter with a small galaxy or massive dark matter structure about 100 million years ago," said Larry Widrow, professor at Queen's University in Canada. "We clearly observe unexpected differences in the Milky Way's stellar distribution above and below the Galaxy's midplane that have the appearance of a vertical wave -- something that nobody has seen before."

The discovery is based on observations of some 300,000 nearby Milky Way stars by the Sloan Digital Sky Survey. Stars in the disk of the Milky Way move up and down at a speed of about 20-30 kilometers per second while orbiting the center of the galaxy at a brisk 220 kilometers per second. Widrow and his four collaborators from the University of Kentucky, the University of Chicago, and Fermi National Accelerator Laboratory have found that the positions and motions of these nearby stars weren't quite as regular as previously thought.

"Our part of the Milky Way is ringing like a bell,' said Brian Yanny, of the Department of Energy's Fermilab. "But we have not been able to identify the celestial object that passed through the Milky Way. It could have been one of the small satellite galaxies that move around the center of our galaxy, or an invisible structure such as a dark matter halo." Adds Susan Gardner, professor of physics at the University of Kentucky:
"The perturbation need not have been a single isolated event in the past, and it may even be ongoing. Additional observations may well clarify its origin."

When the collaboration started analyzing the SDSS data on the Milky Way, they noticed a small but statistically significant difference in the distribution of stars north and south of the Milky Way's midplane. For more than a year, the team members explored various explanations of this north-south asymmetry, such as the effect of interstellar dust on distance determinations and the way the stars surveyed were selected. When those attempts failed, they began to explore the alternative explanation that the data was telling them something about recent events in the history of the Galaxy.

The scientists used computer simulations to explore what would happen if a satellite galaxy or dark matter structure passed through the disk of the Milky Way. The simulations indicate that over the next 100 million years or so, our galaxy will "stop ringing:" the north-south asymmetry will disappear and the vertical motions of stars in the solar neighborhood will revert back to their equilibrium orbits -- unless we get hit again.

The Milky Way is more than 9 billion years old with about 100 billion stars and total mass more than 300 billion times that of the sun. Most of the mass in and around the Milky Way is in the form of dark matter.

Scientists know of more than 20 visible satellite galaxies that circle the center of the Milky Way, with masses ranging from one million to one billion solar masses. There may also be invisible satellites made of dark matter. (There is six times as much dark matter in the universe as ordinary, visible matter.) Astronomers' computer simulations have found that this invisible matter formed hundreds of massive structures that move around our Milky Way.

Because of their abundance, these dark matter satellites are more likely than the visible satellite galaxies to cut through the Milky Way's midplane and cause vertical waves.

"Future astronomical programs, such as the space-based Gaia Mission, will be able to map out the vertical perturbations in our galaxy in unprecedented detail," Widrow said. "That will offer a strong test of our findings."

The results have been published in The Astrophysical Journal Letters:
Lawrence M. Widrow, Susan Gardner, Brian Yanny, Scott Dodelson, and Hsin-Yu Chen "GALACTOSEISMOLOGY: DISCOVERY OF VERTICAL WAVES IN THE GALACTIC DISK"



Media contacts:
Kurt Riesselmann, Fermilab Office of Communication, 630-840-3351, mediafnal.gov

Queen's University
University of Kentucky
The Sloan Digital Sky Survey

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KICP Members: Scott Dodelson
Scientific projects: Sloan Digital Sky Survey (SDSS)

by Donna Weaver and Steve Koppes, The University of Chicago News Office

Seeing is believing, except when you don't believe what you see.

Astronomers using NASA's Hubble Space Telescope have found a puzzling arc of light behind an extremely massive cluster of galaxies residing 10 billion light-years away. The galactic grouping, discovered by NASA's Spitzer Space Telescope, was observed when the universe was roughly a quarter of its current age of 13.7 billion years.

The CARMA (Combined Array for Research in Millimeter Wave Astronomy) also made key observations of the massive galaxy cluster. The University of Chicago is a partner in the CARMA consortium.

The giant arc is the stretched shape of a more distant galaxy whose light is distorted by the monster cluster's powerful gravity, an effect called gravitational lensing. The trouble is, the arc shouldn't exist.

"When I first saw it, I kept staring at it, thinking it would go away," said study leader Anthony Gonzalez of the University of Florida in Gainesville. "According to a statistical analysis, arcs should be extremely rare at that distance. At that early epoch, the expectation is that there are not enough galaxies behind the cluster bright enough to be seen, even if they were 'lensed' or distorted by the cluster.

"The other problem is that galaxy clusters become less massive the farther back in time you go. So it's more difficult to find a cluster with enough mass to be a good lens for gravitationally bending the light from a distant galaxy."

Galaxy clusters are collections of hundreds to thousands of galaxies bound together by gravity. They are the most massive structures in our universe. Astronomers frequently study galaxy clusters to look for faraway, magnified galaxies behind them that would otherwise be too dim to see with telescopes. Many such gravitationally lensed galaxies have been found behind galaxy clusters closer to Earth.

The surprise in these observations is spotting a galaxy lensed by an extremely distant cluster. Dubbed IDCS J1426.5+3508, the cluster is the most massive found at that epoch, weighing as much as 500 trillion suns. It is five to 10 times larger than other clusters found at such an early time in the universe's history.

Astronomers spotted the cluster in a search using NASA's Spitzer Space Telescope in combination with archival optical images taken as part of the National Optical Astronomy Observatory's Deep Wide Field Survey at the Kitt Peak National Observatory in Tucson, Ariz. The combined images allowed them to see the cluster as a grouping of very red galaxies, indicating they are far away.

This unique system constitutes the most distant cluster known to "host" a giant gravitationally lensed arc. Finding this ancient gravitational arc may yield insight into how, during the first moments after the big bang, conditions were set up for the growth of hefty clusters in the early universe.

The arc was spotted in optical images of the cluster taken in 2010 by Hubble's Advanced Camera for Surveys. The infrared capabilities of Hubble’s Wide Field Camera 3 (WFC3) helped provide a precise distance, confirming it to be one of the farthest clusters yet discovered.

Once the astronomers determined the cluster's distance, they used Hubble, the CARMA radio telescope, and NASA's Chandra X-ray Observatory to independently show that the galactic grouping is extremely massive.

CARMA is an excellent observatory for studying such a distant cluster of galaxies because it images the shadow of the cluster against the cosmic microwave background radiation, the fossil light from the big bang, said KICP associate fellow Tom Plagge. This signal is independent of the distance to the cluster, allowing CARMA to quickly and robustly detect massive clusters across the observable universe, if one knows where in the sky to look.

"It was hard to believe they had found such a high-mass cluster at so great a distance, but we knew that CARMA observations would quickly provide a good estimate of its mass," Plagge said.

CARMA helped the astronomers determine the cluster's mass by measuring how primordial light from the big bang was affected as it passed through the extremely hot, tenuous gas that permeates the grouping. The astronomers then used the WFC3 observations to map the cluster's mass by calculating how much cluster mass was needed to produce the gravitational arc. Chandra data, which revealed the cluster's brightness in X-rays, also was used to measure the cluster's mass.

"The chance of finding such a gigantic cluster so early in the universe was less than 1 percent in the small area we surveyed," said team member Mark Brodwin of the University of Missouri-Kansas City. "It shares an evolutionary path with some of the most massive clusters we see today, including the Coma Cluster and the recently discovered El Gordo Cluster."

An analysis of the arc revealed that the lensed object is a star-forming galaxy that existed 10 billion to 13 billion years ago. Gonzalez has considered several possible explanations for the arc, though he remains unconvinced pending further study.

One explanation is that distant galaxy clusters, unlike nearby clusters, have denser concentrations of galaxies at their cores, making them better magnifying glasses. However, even if the distant cores were denser, the added bulk still should not provide enough gravitational muscle to produce the giant arc seen in Gonzalez's observations, according to a statistical analysis.

Another possibility is that the initial microscopic fluctuations in matter made right after the big bang were different from those predicted by standard cosmological simulations, and therefore produced more massive clusters than expected.

The team's results will be published in the July 10 issue of The Astrophysical Journal.

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