KICP in the News, 2018
In 2017, a big year for science, we learned from cosmic discoveries
The Hill, January 11, 2018
Our Universe is unfathomably large - billions of years old, billions of light-years across, and filled with hundreds of billion of galaxies, each with hundreds of billions of stars and planets. It often is beyond the reach of our instruments and our minds. Nonetheless, driven by curiosity, each year we make discoveries that expand our view of it, surprise us and help us to understand our place within it.
The big event of 2017 was the collision of two neutron stars in a relatively nearby galaxy, 140 million light years away. Such events are commonplace, happening many times a day, yet this was one was special because for the first time, the National Science Foundation's Laser Interferometer Gravitational-wave Observatory (LIGO) detected tiny ripples in the fabric of space-time that the cataclysmic event created. LIGO alerted astronomers, and GW170817 became the most well-studied astrophysical event, viewed with radio, infrared, visible, x-ray and gamma-ray "eyes."
Here is but one thing we learned: most, if not all, of the heaviest elements in the periodic table, e.g., gold and platinum, were made by colliding neutron stars.
Of course, LIGO thrilled us in 2016 with its announcement that it had detected gravitational waves from colliding black holes; this past December, three American scientists (Barry Barish and Kip Thorne of Caltech, and Rainer Weiss of MIT) were honored with the Nobel Prize for that discovery.
Closer to home, in October we were surprised by the first interstellar asteroid ever seen. We are used to asteroids - debris left over from the formation of our solar system - visiting us. In fact, the PanSTARRS1 telescope on Haleakala that discovered Oumuamua (for "scout"), as it is now officially known, searches for near-Earth objects that are potentially Earth-threatening. Oumuamua is not bound to our sun; it flew in from the direction of the Lyra constellation, passed between Mercury and the sun, and flew out again in the direction of the Pegasus constellation.
As large as an aircraft carrier and similarly shaped, Oumuamua reminded us that we are connected to the rest of the cosmos. Our solar system likely has shed asteroids and even planets that have flown by other stars with planets, and four NASA spacecraft - Pioneers 10 and 11 and Voyagers 1 and 2 - have left our solar system. The Voyagers carry the Golden Record of sounds recorded from Earth that Carl Sagan and his team put together to introduce us to the larger Universe.
It has been more than 20 years since we discovered the first exoplanets (planets orbiting around other stars). NASA's Kepler satellite has been the exoplanet workhorse, having discovered more than 4,000 exoplanets and 600 planetary systems. Astronomers have identified around 10 exoplanets in the habitable zone. Last year's big news was the discovery of the TRAPPIST 1 system, seven terrestrial-like planets orbiting a red dwarf star about 40 light years away. Five of the seven planets are similar in size to Earth and three are in the habitable zone, the sweet spot where liquid water - and hopefully life - can exist. We are well on our way to answering a very big question: Are we alone?
Moving to the far reaches of the Universe, the most distant quasar seen yet was discovered last year. The light we see began the journey to us when the Universe was only about 700 million years old. It presents us with a mystery: How did the billion-solar-mass black hole that powers this quasar form so early in the history of the Universe? (All galaxies, including our Milky Way, have massive black holes at their centers and go through an early "quasar phase" when their black holes shine brightly because of infalling matter.) LIGO and other gravitational-wave detectors coming on line in the future should shed light on this question.
While the great American eclipse of 2017 was not a surprise and did not lead to any startling discoveries, millions of Americans including me - were awed by it as the path of totality traversed the United States from Oregon to Georgia. In this amazing natural phenomenon, the moon nicely fits over the sun and blocks its light, allowing us to look directly at the sun without being blinded and view its - beautiful corona.
The corona of the sun is much hotter (millions of degrees) and wispier than its surface, extending many solar radii beyond the disk of the sun. The corona is responsible for much of the sun's activity that impacts our planet, including solar flares and coronal mass ejections, and how the corona works is still a mystery. Later this year, NASA will launch the Parker Solar Probe, which will orbit the sun on a highly elliptical path that will take it inside the sun's corona - really! - more than 20 times to make measurements that could solve some of mysteries of the corona.
Science is now a global activity that the United States no longer dominates. But as these discoveries illustrate, we continue to lead. Our success has involved three critical elements: thinking bold, throwing deep and sticking with it.
The LIGO Nobel Laureates were bold enough to think that you could detect a change in distance of one-thousandth the size of a proton between two mirrors separated by four kilometers. The NSF threw deep when it invested close to $1 billion over 25 years to build LIGO. And NASA stuck with it when Hubble had initial mirror problems, and more recently when it found a work-around to keep Kepler producing science after two gyros failed at the end of its four-year planned mission.
Certainly, cosmic discoveries help us to understand our place in the Universe, but they also inspire and awe us, young and old.
Michael S. Turner is a theoretical cosmologist who coined the term "dark energy" in 1998. He is the Bruce V. and Diana M. Rauner Distinguished Service Professor at the University of Chicago, and is the former assistant director for mathematical and physical sciences for the National Science Foundation.
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KICP Members: Michael S. Turner
Scientific projects: Laser Interferometer Gravitational-wave Observatory (LIGO)
Dark Energy Survey finds remains of 11 galaxies eaten by the Milky Way
UChicago News, January 16, 2018
Scientific collaboration including UChicago and labs releases three years of data
Scientists have released the preliminary cosmological findings from the Dark Energy Survey - research on about 400 million astronomical objects, including distant galaxies as well as stars in our own galaxy.
Among the highlights of the first three years of survey data, presented Jan. 10 during the American Astronomical Society meeting in Washington, D.C., is the discovery of 11 new stellar streams - remnants of smaller galaxies torn apart and devoured by our Milky Way.
The results were announced by the Dark Energy Survey, an international collaboration of more than 400 members including scientists from UChicago, Argonne and Fermilab, that aims to reveal the nature of the mysterious force of dark energy.
The public release fulfills a commitment scientists on the survey made to share their findings with the astronomy community and the public. The data cover about 5,000 square degrees, or one-eighth of the entire sky, and include roughly 40,000 exposures taken with the Dark Energy Camera. The images correspond to hundreds of terabytes of data and are being released along with catalogs of hundreds of millions of galaxies and stars.
"There are all kinds of discoveries waiting to be found in the data," said Brian Yanny of Fermi National Accelerator Laboratory, Dark Energy Survey data management project scientist. "While DES scientists are focused on using it to learn about dark energy, we wanted to enable astronomers to explore these images in new ways, to improve our understanding of the universe."
The Dark Energy Camera, the primary observation tool of the Dark Energy Survey, is one of the most powerful digital imaging devices in existence. It was built and tested at UChicago-affiliated Fermilab, the lead laboratory on the Dark Energy Survey, and is mounted on the National Science Foundation's 4-meter Blanco telescope in Chile. The DES images are processed by a team at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.
One new discovery enabled by the data set is the detection of 11 new streams of stars around our Milky Way. Our home galaxy is surrounded by a massive halo of dark matter, which exerts a powerful gravitational pull on smaller, nearby galaxies. The Milky Way grows by pulling in, ripping apart and absorbing these smaller systems. As stars are torn away, they form streams across the sky that can be detected using the Dark Energy Camera. Even so, stellar streams are extremely difficult to find since they are composed of relatively few stars spread out over a large area of sky.
"It's exciting that we found so many stellar streams," said astrophysicist Alex Drlica-Wagner of Fermilab and the Kavli Institute for Cosmological Physics at UChicago. "We can use these streams to measure the amount, distribution and 'clumpiness' of dark matter in the Milky Way. Studies of stellar streams will help constrain the fundamental properties of dark matter."
Prior to the new discoveries, only about two dozen stellar streams had been discovered. Many of them were found by the Sloan Digital Sky Survey, a precursor to the Dark Energy Survey. The effort to detect new stellar streams in the Dark Energy Survey was led by University of Chicago graduate student Nora Shipp.
"We're interested in these streams because they teach us about the formation and structure of the Milky Way and its dark matter halo. Stellar streams give us a snapshot of a larger galaxy being built out of smaller ones," said Shipp. "These discoveries are possible because DES is the widest, deepest and best-calibrated survey out there."
Since there is no universally accepted naming convention for stellar streams, the Dark Energy Survey has reached out to schools in Chile and Australia, asking young students to select names. Students and their teachers have worked together to name the streams after aquatic words in native languages from northern Chile and aboriginal Australia.
Funding: U.S. Department of Energy Office of Science, National Science Foundation
- This release was originally posted on the Fermi National Accelerator Laboratory website.
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KICP Members: Alex Drlica-Wagner
KICP Students: Nora Shipp
Scientific projects: Dark Energy Survey (DES)
Stephen Hawking: A physicist's appreciation
Bulletin of the Atomic Scientists, March 16, 2018
Stephen Hawking was a singular individual, revered both by his fellow scientists and by the public. His books were bestsellers, his public lectures were always standing-room-only, and as a sign of his broad appeal, he appeared in Star Trek, The Simpsons, and The Big Bang Theory. He became a household name. Hawking was passionate about his science, but also passionate about sharing his unique insights with the world.
His scientific legacy is assured. I believe his discovery that black holes have a temperature is one of the most beautiful and profound accomplishments of humankind, bar none. Hawking presented his results in a paper titled "Particle creation by black holes." This relatively innocuous title hides a revolution in physics. The paper is staggeringly perfect, combining physical insight with technical mastery, and is thrilling to read even 40 years later and will remain so for the foreseeable future.
Black holes are the most extreme objects in the universe, regions where the gravity is so strong that nothing can escape. Hawking showed that when you add quantum mechanics, the uncertainty principle results in particles appearing to leak out of the black holes, and thus black holes have a temperature. Black holes aren't truly black! This is a beautiful result, vividly demonstrating the unity of physics, while hinting at some underlying, fundamental processes that we have yet to understand. Because black holes radiate particles, they must lose mass, in a process known as black hole evaporation. As the black holes radiate they get smaller, and thus hotter, meaning that they radiate energy faster, and thus get even smaller and even hotter, and so on. The result is that all black holes eventually explode! Hawking radiation is still at the very forefront of theoretical physics. There are raging debates about how Hawking radiation actually works, and whether it somehow carries away the information of how the black hole was formed. One of the greatest mysteries in physics is what is left behind after Hawking radiation causes a black hole to fully evaporate.
I met Hawking a few times over the years, including at the University of Cambridge and the University of Chicago. In addition to scientific discussions, I participated in Stephen Hawking's Universe, a six-part TV documentary about the birth and evolution of the universe, black holes, and other important aspects of modern cosmology. One of my most memorable interactions with him was from when I was a post-doctoral fellow at the Kavli Institute for Cosmological Physics in Santa Barbara. Hawking visited and sat across the hall from me for two weeks. It was wonderful to spend an extended period of time with him and appreciate his insights, intuition, and, especially, his humor.
One memory is particularly vivid: I described a project I had been working on for months; it had to do with how light travels in the universe. After listening politely, he responded with several statements I initially found inscrutable. I went back to my office somewhat deflated; it seemed clear he hadn't understood what I had been describing. But I continued to contemplate his comments and over the course of the ensuing weeks it slowly dawned on me that not only had he understood, but he had jumped way past me, providing signposts, far off in the distance, that pointed toward a deeper understanding of the subject. It took me months to fully discover and appreciate the entire meaning of his comments.
When he wasn't exploring the far reaches of the universe, Hawking actively engaged with the here and now. His was a voice that transcended politics, urging us to fully appreciate the world around us and to maintain a healthy perspective, given the immensity of the cosmos. In his later years, Hawking became increasingly alarmed about the potential for human-induced global catastrophe. He helped found the Breakthrough Starshot initiative to try to develop prototypes for interstellar travel; part of his motivation was to develop a back-up plan if the Earth becomes inhospitable. He also joined the Board of Sponsors of the Bulletin of Atomic Scientists and was a particularly vital and valued member. When the Bulletin moved the minute hand of the Doomsday Clock closer to midnight in 2007, Hawking said, "As scientists, we understand the dangers of nuclear weapons and their devastating effects, and we are learning how human activities and technologies are affecting climate systems in ways that may forever change life on Earth. As citizens of the world, we have a duty to alert the public to the unnecessary risks that we live with every day, and to the perils we foresee if governments and societies do not take action now to render nuclear weapons obsolete and to prevent further climate change."
The ensuing decade has made Hawking's exhortation ever more relevant and urgent. We ignore him at our peril.
Hawking has left the universe a much more interesting place than he found it.
Daniel Holz is an Associate Professor in Physics, Astronomy & Astrophysics, the Enrico Fermi Institute, and the Kavli Institute for Cosmological Physics, at the University of Chicago. His research focuses on general relativity in the context of astrophysics and cosmology. He is a member of the Laser Interferometer Gravitational-Wave Observatory (LIGO) collaboration, and was part of the team that announced the first detection of gravitational waves in early 2016. He received a 2012 National Science Foundation CAREER Award, the 2015 Quantrell Award for Excellence in Undergraduate Teaching, and the Breakthrough Prize in Fundamental Physics in 2016, and was selected as a Kavli Fellow of the National Academy of Sciences in 2017. Holz received his PhD in physics from the University of Chicago and his AB in physics from Princeton University.
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KICP Members: Daniel E. Holz
2018 APS Medal for Exceptional Achievement in Research
APS News, March 20, 2018
The 2018 APS Medal for Exceptional Achievement in Research was awarded on February 1 to Eugene Parker, professor emeritus at the University of Chicago, for his "many fundamental contributions to space physics, plasma physics, solar physics, and astrophysics during the past 60 plus years." (Top Left) The medal was presented to Parker by 2018 APS President Roger Falcone along with APS CEO Kate Kirby. (Top Right) Family members and colleagues joined in the celebration: from left to right, Eric Parker, Susan Kane-Parker, Niesje Parker, Eugene Parker (seated); Michael Turner, Rocky Kolb, and Young-Kee Kim (University of Chicago), and Timothy Gay (University of Nebraska-Lincoln, APS Speaker of the Council, and University of Chicago Ph.D. graduate). APS is accepting nominations for the 2019 APS Medal now through May 1.
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KICP Members: Edward W. Kolb; Michael S. Turner
Cosmologists Can't Agree on the Hubble Constant
American Physical Society, April 23, 2018
The discrepancy in measures of the Hubble constant, which quantifies the expansion of the Universe, has only grown in recent years.
The Hubble constant H0 tells us the speed at which galaxies are receding from us as the Universe expands. Over the past five years, cosmologists have recognized that there is a discrepancy between different measurements of this fundamental parameter. Three speakers in a session at the April Meeting of the American Physical Society in Columbus, Ohio, discussed the status of this "crisis in cosmology." The field has now accepted that the problem is real, and some researchers are optimistic that it could lead to important discoveries.
The problem began in 2013, when the first results were reported from the Planck satellite, which had measured the cosmic microwave background (CMB). The Planck team's value for H0 was 67.±1.2 kilometers per second per megaparsec (km/s/Mpc), lower than previous measurements, which had been between 70 and 75 km/s/Mpc. The result also had error bars small enough that even this slight difference was a potential problem. Planck's 2015 result was not very different, though it came with even smaller error bars.
Prior to the Planck announcement, the Supernova H0 for the Equation of State (SH0ES) Collaboration, led by Adam Riess of Johns Hopkins University in Baltimore, had already set out to make a measurement ofH0 in our cosmic neighborhood with higher precision than previous efforts. The researchers focused on re-calibrating three of the standard distance-measuring techniques from scratch - the motion of stars due to Earth's orbit (parallax), pulsating stars known as Cepheid variables, and Type Ia supernovae, said team member David Jones of the University of California at Santa Cruz. Based on their improved distance measures, SH0ES reported an H0 value of 73.2 ± 1.7 km/s/Mpc in 2016. This result differed from Planck's by more than 3 standard deviations, a highly statistically significant difference that could not easily be explained.
Re-analyses of the SH0ES results confirmed the 2016 finding, as did additional measurements of H0 in the local Universe. But an independent H0 determination in 2016 based on so-called baryon acoustic oscillations - the sloshing of matter in the early Universe that produced the characteristic CMB patterns - lined up with the Planck result.
Stephen Feeney of the Flatiron Institute in New York said that despite quite a bit of attention to the issue, no one has found any problems with the measurements that could have a large enough effect to close the gap. Cosmologists have also been discussing whether the standard cosmological model, known as ΛCDM, may require modification. This theory is used for the CMB-based determinations of H0. But the proposed adjustments to ΛCDM all introduce at least some conflicts with other types of data. Feeney estimates that the odds are 60:1 that all of the data could be explained by statistical flukes and ΛCDM alone.
Last year, the Planck team performed a more detailed analysis of their data and found that the CMB fluctuations on the smallest angular scales had the largest effect on lowering H0. Describing these results, Bradford Benson of Fermilab said that when the team used only their data from larger angular scales (above about 0.2o), they derived an H0 value consistent with the SH0ES result.
According to Benson, the smaller angular scales provide a more sensitive test of a particular parameter in ΛCDM than larger scales. The parameter is the density of neutrinos in the Universe, which should be proportional to the number of neutrino species (there are three in the standard model of particle physics). Increasing the number of neutrino types is one of the few ways to reasonably tweak ΛCDM and increase Planck's H0 enough to close the gap with local measurements. However, this solution would also require more massive neutrinos to avoid disagreements with other cosmological data sets, said Benson. And of course, there isn't much evidence for a fourth neutrino type.
Jones, Feeney, and Benson agreed that the discrepancy isn't going away and that more data are essential to explain it. The expected future trove of gravitational waves from binary neutron star mergers, for example, will provide independent estimates for H0. (Last year's event led to a value somewhere between those of Planck and SH0ES but with much larger error bars.) In addition, the South Pole Telescope and the Atacama Cosmology Telescope have upgraded equipment that will soon provide better CMB maps, and the Gaia satellite will provide a new level of precision parallax measurements.
Benson thinks there's a good chance that a "benign" explanation will solve the problem. However, in a different session, Riess pointed out that problems with the value of H0 have led to great discoveries in the past, including the existence of dark energy.
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KICP Members: Bradford A. Benson
Scientific projects: South Pole Telescope (SPT)
Big Brains podcast explores how world's largest telescope might glimpse universe's birth
UChicago News, May 15, 2018
Cosmologist Wendy Freedman on how new technology could lead to major discoveries
Prof. Wendy Freedman spent much of her career measuring the age of the universe. Now she's working on a project that may very well give scientists a chance to glimpse into its birth.
Freedman, the John & Marion Sullivan University Professor of Astronomy & Astrophysics, works in the field of observational cosmology, measuring the expansion rate of the universe. In 2001, she and a team of scientists found that the universe is around 13.7 billion years old -- far more precise than the previous estimate in the 10- to 20-billion-year-old range.
Freedman was the founding leader from 2003 until 2015 of an international consortium of researchers and universities (including UChicago) to build the world's largest telescope high in the mountains of Chile. The Giant Magellan Telescope will be as tall as the Statue of Liberty when complete, and ten times more powerful than the Hubble Space Telescope -- with the ability to look back at the dawn of the cosmos.
"In our field, the new developments have come with new technology," Freedman said. "Without exception, from the time that Galileo first turned a telescope to the sky in 1609, every time we've built a new capability we've made new discoveries, which is why we're so excited about this."
The telescope, 80 feet in diameter and weighing more than 20 tons, will be the first of its kind to see fine details like a planet's atmosphere, which could one day help discover life on other planets. The telescope is expected to be operational starting in 2024.
"If we really were able to show that there's life on a planet outside of our own solar system, that will be one of the discoveries that will not only be exciting for astronomers but will change human kindís perspective on our place in the universe," Freedman said.
On this episode of Big Brains, Freedman discusses her research on measuring the age of the universe, her leadership of the Giant Magellan Telescope and the search for life outside our solar system.
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KICP Members: Wendy L. Freedman
Scientific projects: Giant Magellan Telescope (GMT)