September 28, 2016 | 3:30 PM | ERC 161 | Astronomy Colloquium Towards the identification of Earth-like worlds with MAROON-X Jacob Bean, University of Chicago
Exoplanet surveys have recently progressed to the point of discovering small, potentially terrestrial planets orbiting in circumstellar habitable zones. Assessing the true degree of habitability of these worlds requires gaining knowledge of both their bulk and atmospheric properties. In this talk I will present my group's work to make advances on these subjects. I will begin wit an overview of recent results from exoplanet atmosphere observations with an emphasis on results from major program using the Hubble and Spitzer Space Telescopes. I will then summarize the development of MAROON-X, which is a high precision radial velocity spectrograph designed to measure the masses, and thus constrain the densities of potentially Earth-like worlds. I will describe how MAROON-X will be used in conjunction with future facilities like TESS, JWST, and the GMT to make the first credible searches for habitable environments beyond our Solar System.
October 5, 2016 | 3:30 PM | ERC 401 (Note new location) | Astronomy Colloquium Planets around Binary Stars Dan Fabrycky, University of Chicago
Planet formation and evolution around single stars seemed hard enough. Now gas giant planets have been found orbiting binary stars, bringing new challenges and opportunities regarding the theory of planet formation and evolution. First we will review the discoveries of a dozen planets by NASA's Kepler mission, using both the transit and the timing methods. These discoveries prove that planets can tiptoe near the instability zone; the specific dynamical arrangements offers clues into migration of planets through gaseous disks. Planets seem to avoid coming near very close binaries, which is a new data point relating to the dynamical history of such binaries. That some planets went unstable is very likely, and we consider the fate of such planets as well as observational signatures.
October 12, 2016 | 3:00 PM | ERC 161 | Wednesday colloquium The Dark Energy Survey and Gravitational Waves Marcelle Soares-Santos, Fermilab
PDF | Video In this talk I present recent results of the Dark Energy Survey (DES) searches for optical counterparts to Gravitational Wave (GW) events detected by the LIGO/Virgo Collaboration. Our program achieved greater sensitivity than any other optical facility last year. For the second observing campaign (Fall/2016-Spring/2017) our goals are to either make a detection or establish significant constraints on optical emission from such events. DES is the greatest optical imaging survey yet, aiming at percent-level precision measurements of cosmological parameters from a combination of probes such as type Ia supernovae, galaxy clusters, and weak gravitational lensing. These probes are limited by astrophysical systematics and new independent methods are required in order to beat systematic effects down to sub-percent levels. Standard sirens, events for which distances are determined from their gravitational wave signal, are one possible new method to meet that challenge. Our program will potentially have a great impact in our field by exploring this possibility from the observational perspective. In this talk I will also briefly discuss this exciting prospect for future observing campaigns.
October 19, 2016 | 3:30 PM | ERC 161 | Astronomy Colloquium Protostellar Disks: Formation and Polarization Zhi-Yun Li, Virginia
Circumstellar disks play a central role in the formation of both stars and planets, but how they form remains uncertain. Once thought to be a simple consequence of the conservation of angular momentum during the hydrodynamic collapse of molecular cloud cores, disk formation is now known to be complicated by the presence of a dynamically important magnetic field, which can strongly brake the rotation. Indeed, both analytic arguments and numerical simulations have shown that protostellar disk formation is suppressed in the ideal MHD limit for the observed level of cloud core magnetization. In the first part of the talk, I will discuss the physical reason for this so-called "magnetic braking catastrophe" in disk formation, and review possible ways to avert it, including non-ideal MHD effects, misalignment between the magnetic field and rotation axis, and turbulence. In the second part, I will discuss the millimeter polarization recently detected in the disk of the famous young stellar object HL Tau, focusing on possible contribution from scattering by large dust grains. If confirmed, the dust scattering-induced polarization would open a new window on grain growth, the crucial first step toward the formation of planetesimals and eventually planets. The field of disk polarization is poised for rapid growth in the ALMA era.
October 26, 2016 | 3:30 PM | ERC 161 | Wednesday colloquium The First Four Months of Gravitational Wave Astronomy Ben Farr, Enrico Fermi Institute and KICP
PDF | Video On September 14, 2015 LIGO made the first direct detection of gravitational waves, marking the beginning of gravitational wave astronomy. The LIGO instruments continued to take data over the next four months, completing their first observing run on January 19, 2016 with 51.5 days of coincident data. I will present results from advanced LIGO's first four months of operation, and what they have taught us thus far.
November 2, 2016 | 3:30 PM | ERC 161 | Astronomy Colloquium Black Hole Physics with the Event Horizon Telescope Feryal Ozel, University of Arizona
The Event Horizon Telescope is an experiment that is being performed on a large and ever-increasing array of radio telescopes that span the Earth from Hawaii to Chile and from the South Pole to Arizona. When data will be taken with the full array, it will image the event horizons of the supermassive black hole at the center of our Galaxy, Sagittarius A*, and the black hole at the center of M87, with an unprecedented 10 microarcssecond resolution. This will allow us to take the first ever pictures of black holes at 1.3 and 0.85 mm wavelengths and look for the shadow that is a direct evidence for a black hole predicted by the theory of General Relativity. In addition, the Event Horizon Telescope will also enable us to study the process by which black holes accrete matter and grow in mass. I will discuss the theoretical developments in simulating the properties of the black hole accretion flows and their expected images using state-of-the-art algorithms and high performance computing. Interpreting the upcoming observations within this theoretical framework will open new horizons in black hole astrophysics.
November 9, 2016 | 3:30 PM | ERC 161 | Wednesday colloquium New Directions in Searching for the Dark Universe Surjeet Rajendran, UC Berkeley
PDF | Video Observational bounds currently permit the existence of a large number of dark matter candidates, ranging from ultra-light axions with masses ~ 10^(-22) eV to MACHOs with mass as large as 10^(24) gm. It is important to develop experimental methods to constrain this vast range of parameters. In this talk, I will describe new experimental methods to probe a wide variety of dark matter candidates, ranging from ultra-light axions with masses ~ 10^(-22) eV to light WIMPs with mass in the keV - GeV range. A variety of precision measurement technologies such as optical/atomic interferometry and SQUID magnetometry can be applied to search for these particles. I will also discuss methods to search for the direction of the nuclear recoil induced by conventional WIMP scattering in detectors with solid state densities. These directional detectors may enable probes of conventional WIMP dark matter beyond the solar neutrino floor.
November 16, 2016 | 3:30 PM | ERC 161 | Astronomy Colloquium Where are we in the hunt for the core collapse supernova explosion mechanism(s)? Anthony Mezzacappa, Joint Institute for Computational Sciences, Oak Ridge National Laboratory
Fifty years have passed since the first simulations of core collapse supernovae were performed. Definitive simulations that assumed spherical symmetry have been completed, and laid the foundation for simulations in two spatial dimensions that assume axial symmetry and three spatial dimensions with no imposed symmetries. In the past decade, axially symmetric simulations of core collapse supernovae have matured rapidly, and three-dimensional simulations have been initiated in earnest. Progress has in fact been exponential given the derived understanding from past work and the availability of increasing computational capability. I will discuss what has been illuminated as central to the explosion mechanism to date, the current state of the community's simulation efforts, and the requirements and challenges that lie ahead in order to perform definitive three-dimensional simulations that will pin down the recipe for explosion and provide a predictive capability for all of the observables associated with core collapse supernovae. The timeliness of this progress and future push are highlighted by the recent birth of gravitational wave astronomy. The next Galactic supernova promises a wealth of information for supernova modelers and members of the gravitational wave, neutrino, and nuclear physics communities.
November 30, 2016 | 3:30 PM | ERC 161 | Astronomy Colloquium Planet Nine from Outer Space Konstantin Batygin, Caltech
At the outskirts of the solar system, beyond the orbit of Neptune, liesan expansive field of icy debris known as the Kuiper belt. The orbits of the individual asteroid-like bodies within the Kuiper belt trace out highly elongated elliptical paths, and require hundreds to thousands of years to complete a single revolution around the Sun. Although the majority of the Kuiper belt's dynamical structure can be understood within the framework of the known eight-planet solar system, bodies with orbitalperiods longer than about 4,000 years exhibit a peculiar orbital alignment that eludes explanation. What sculpts this alignment and how is it preserved? In this talk, I will argue that the observed clustering of Kuiperbelt orbits can be maintained by a distant, eccentric, Neptune-like planet, whose orbit lies in approximately the same plane as those of the distant Kuiper belt objects, but is anti-aligned with respect to those of the small bodies. In addition to accounting for the observed grouping of orbits, the existence of such a planet naturally explains other, seemingly unrelated dynamical features of the solar system.
December 7, 2016 | 3:30 PM | ERC 161 | Wednesday colloquium Increasing Accuracy and Increasing Tension in H0 Wendy Freedman, KICP
PDF | Video The accuracy in direct measurement of distances to galaxies has continued to improve dramatically over the past decade. Local measurements of the Hubble constant based on Hubble Space Telescope observations of astrophysical standard candles -- Cepheids and Type Ia supernovae -- have converged on a value of about 73 km/sec/Mpc with an uncertainty of 2-3%. At the same time, estimates assuming a Lambda-CDM standard model and fitting highly precise measurements of cosmic microwave background fluctuations have yielded a value of Ho = 67 km/sec/Mpc. The two methods disagree at approximately the 3-sigma level. The reason for this discrepancy is not understood at present, and new data have only increased the tension. If real, the disagreement could be signaling missing physics in the standard model; for example, additional dark radiation. Major efforts are ongoing to improve further the accuracy in the local measurements, including developing other techniques to test the Cepheid distance scale. In the near future JWST and Gaia will provide a path to measuring Ho to 1%, comparable to the precision in CMB measurements.
September 30, 2016 | 12:00 PM | ERC 401 | Friday noon seminar Towards precision cosmology with large scale structures: the halo model and perturbative approaches Irshad Mohammed, Fermilab
The theoretical modeling of the statistical observables of the large-scale structures of the Universe, like galaxy clustering, weak lensing etc., is necessary in order to derive any constraints on the cosmological parameters. One of the most important ingredients of the theoretical model is the two-point correlation function, or its Fourier transform the matter power spectrum. I will discuss the precision in its calculations based on a modified halo model, and the systematic effects due to the baryonic processes. Further, I will also discuss the covariance matrix of the matter power spectrum and its estimators based on the halo model and the perturbation theory. We find the agreement with the simulations is at a 10% level up to k ∼ 1 h/Mpc. We show that all the connected components are dominated by the large-scale modes (k < 0.1h/Mpc), regardless of the value of the wavevectors of the covariance matrix. Finally, I will provide a prescription for how to evaluate the covariance matrix from small box simulations without the need to simulate large volumes.
October 7, 2016 | 12:00 PM | ERC 401 | Friday noon seminar Preparing for the 21cm future - lessons from the Bleien Galactic Survey project Chihway Chang, UofC
HI intensity mapping is emerging as a new and promising cosmological probe for both the large-scale structure and the early Universe. In preparation for the many large radio projects that are coming online, we launched the Bleien Galactic Survey project as an exercise to test new (and fun) techniques that could develop into useful tools in future surveys. I will first introduce the background science and basic setup of the experiment, and then touch upon two particularly interesting ideas - calibrating the telescope beam using drones, and RFI mitigation with start-of-the-art deep learning algorithms.
October 14, 2016 | 12:00 PM | ERC 401 | Friday noon seminar Partially Acoustic Dark Matter, Interacting Dark Radiation, and Large Scale Structure Yuhsin Tsai, University of Maryland
The standard paradigm of collisionless cold dark matter is in tension with measurements on large scales. In particular, the best fit values of the Hubble rate and the matter density perturbation inferred from the CMB seem inconsistent with the results from direct measurements. In this talk, I will discuss these issues and propose a solution to both problems from a dark sector that contains dark acoustic oscillations with dark fluid. Such a solution can be tested by future experiments designed to probe the CMB and large scale structure.
October 21, 2016 | 12:00 PM | ERC 401 | Friday noon seminar SPIDER: Exploring the dawn of time from above the clouds Jeffrey P Filippini, University of Illinois, Urbana-Champaign
Inflation is thought to have seeded the cosmos with a hum of primordial gravitational waves - unique messengers from the universe's earliest moments. These ripples in spacetime should have left a unique "B-mode" signature on the polarization of the cosmic microwave background. SPIDER is a powerful balloon-borne instrument designed to tease out this polarization pattern in the presence of galactic foregrounds. I will give an update from SPIDER's successful long-duration balloon flight over the Antarctic ice in January 2015, including performance estimates and the current status of the analysis, as well as a status report on payload development for SPIDER's upcoming second flight.
October 28, 2016 | 12:00 PM | ERC 401 | Friday noon seminar ADMX (Axion Dark Matter eXperiment) Ian P Stern, University of Florida
Nearly all astrophysical and cosmological data point convincingly to a large component of cold dark matter (CDM) in the Universe. The axion particle, first theorized as a solution to the strong charge-parity problem of quantum chromodynamics, has been established as a prominent CDM candidate. Cosmic observation and particle physics experiments have bracketed the unknown mass of CDM axions between approximately a μeV and a meV.
The Axion Dark Matter eXperiment (ADMX) is a direct-detection CDM axion search which has set limits at the KSVZ coupling of the axion to two photons for axion masses between 1.9 and 3.7 μeV. ADMX has recently begun conducting searches with an upgraded detector, which will allow for detection at even the most pessimistic couplings within this mass range. In order to expand the mass reach of the detector, ADMX is conducting extensive research and development of microwave cavity technology. Status of the experiment, current research, and projected sensitivities will be presented.
November 4, 2016 | 12:00 PM | ERC 401 | Friday noon seminar Dark Matter Radio (Hidden Photons/Axions) Arran Phipps, Stanford University
Determining the composition of dark matter is at the forefront of modern scientific research. There is compelling evidence for the existence of vast quantities of dark matter throughout the universe, however it has so-far eluded all direct detection efforts and its identity remains a mystery. While weakly interacting massive particles (WIMPs) are a favored candidate and have been the primary focus of direct detection for several decades, there has been recent interest in searching for ultra light field dark matter. The Dark Matter Radio is a tunable superconducting high-Q lumped-element resonator (read out with SQUIDs) being built to search for sub-eV hidden photon and axion dark matter. I will discuss the motivation, detection strategy, design, and current status of the DM Radio experiment.
November 11, 2016 | 12:00 PM | ERC 401 | Friday noon seminar Cooling and AGN heating in cool-core galaxy clusters Yuan Li, University of Michigan
The feedback from active galactic nuclei (AGNs) is widely considered to be the major heating source in cool-core galaxy clusters, preventing a classical cooling flow where the intra-cluster medium (ICM) cools at hundreds to a thousand solar masses per year. We perform adaptive mesh simulations using Enzo including both momentum-driven AGN feedback and star formation to study the interplay between ICM cooling, AGN heating and star formation over 6.5 Gyr in an isolated cool-core cluster. We find that AGN jets globally heat up the ICM via weak shock waves and turbulence. Locally, cold clumps can cool out of the ICM due to the non-linear perturbation driven by the AGN jets. These cold clumps feed both star formation and the supermassive black hole (SMBH), triggering an AGN outburst which increases the entropy of the ICM and reduces its cooling rate. When star formation completely consumes the cold gas, leading to a brief shutoff of the AGN, the ICM quickly cools and develops multiphase gas again, followed by another cycle of star formation/AGN outburst. The simulation reproduces a wide range of observed properties and naturally explain the variety of star forming clouds observed in the center of cool-core clusters.
November 18, 2016 | 12:00 PM | ERC 401 | Friday noon seminar Substantial Variation in the Stellar Halos of Spiral Galaxies Allison Merritt, Yale University
The Dragonfly Telephoto Array, comprised of 48 individual Canon telephoto lenses operating together as a single telescope, is an innovative approach to low surface brightness imaging. Sub-nanometer coatings on each optical element reduce scattered light from nearby bright stars and compact galaxy centers -- typically a key obstacle for integrated light observations -- by an order of magnitude, and Dragonfly's large field of view (2 x 2.6 degrees for a single frame) provides a large-scale view of galactic stellar halos and satellite systems. Using extremely deep (>30 mag/arcsec^2) optical imaging in g and r bands from the Dragonfly Nearby Galaxies Survey (DNGS), we have characterized the stellar halos of a sample of nearby luminous galaxies. I will present measurements of the stellar halo mass fractions of an initial sample of spiral galaxies from the survey, and discuss these in the context of the assembly histories of individual galaxies.
December 9, 2016 | 12:00 PM | ERC 401 | Friday noon seminar Solid-state imaging detectors for low-energy particle physics Alvaro Chavarria, The University of Chicago
The low noise, high spatial resolution and reliable performance of charge-coupled devices (CCDs) and complementary metal-oxide-semiconductor (CMOS) active pixel arrays have made them detectors of choice for digital imaging, from consumer electronics to state-of-the-art astronomical cameras. Although the slow time response of these devices has limited their application in high-energy particle physics, for the case of rare-event searches, where the particle interaction rate is extremely low, their properties can be fully exploited to build detectors that outperform in many aspects the traditional technologies of the field. I will present recent results from the DAMIC experiment, a low-mass dark matter search consisting of low-noise CCDs deployed in the SNOLAB laboratory. I will show how the exquisite spatial resolution of the detector allows for particle identification, and provides the unique capability to reject sequences of radioactive decay with utmost efficiency. These techniques can be extended to the field of neutrinoless double beta decay. I will present a recent proposal where we argue that a large array of amorphous Se-82 imagers based on CMOS technology could achieve the background requirements necessary to test if neutrinos are Majorana fermions even in the case of a normal hierarchy of neutrino masses.
October 25, 2016 | 12:00 PM | ERC 576 | Tuesday Seminar The Late-Time Formation and Dynamical Signatures of Small Planets Eve Lee, UC Berkeley
The Kepler mission has established that approximately half of all Sun-like stars harbor planets. Of these, close-in super-Earths are the most common. Understanding the origin of super-Earths can lend us insight into the default pathway of planet formation. The riddle posed by super-Earths is that they are not Jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-Earths accreted atmospheres that weigh only a few percent of their total mass. I will show that this puzzle is solved if super-Earths formed late, in the inner cavities of transitional disks. Super-puffs present the inverse problem of being too voluminous for their small masses. I will show that super-puffs most easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside 1 AU, and then migrate in just after super-Earths appear. Small planets may remain ubiquitous out to large orbital distances. I will demonstrate that the variety of debris disk morphologies revealed by scattered light images can be explained by viewing an eccentric disk, secularly forced by a planet of just a few Earth masses, from different observing angles. The farthest reaches of planetary systems may be perturbed by eccentric super-Earths.
November 15, 2016 | 12:00 PM | ERC 576 | Tuesday Seminar The Power Law in the Radio Sky Siyao Xu, Peking University, Bejing
As shown by overwhelming observational evidence, the interstellar medium (ISM) is turbulent and magnetized. The ubiquitous magnetized turbulence in the ISM connects the physical processes happening on local small scales (~10^7 cm) to global large scales (~ 100 pc), through the power-law spectrum of turbulence. The turbulent spectrum has been measured in both the warm ionized medium, known as "the big power law in the sky", and cold neutral medium. The power-law nature of the interstellar turbulence is widely imprinted in fluctuating observables in the ISM. An in-depth understanding of the power-law statistics of magnetized turbulence is the key to unlocking many mysteries in radio observations that have been puzzling for decades. These observables in turn provide valuable information on interstellar turbulence and density distribution in a straightforward way. In the light of radio observations of Galactic pulsars, I will show you what I have seen in our room, i.e., the Galactic ISM, and in the fast radio burst's room, extragalactic ISM.
November 22, 2016 | 12:00 PM | ERC 576 | Tuesday Seminar The Destructive Birth of Massive Stars and Massive Star Clusters Anna Lorraine Rosen, University of California, Santa Cruz
Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject with their intense radiation fields and stellar winds into the interstellar medium (ISM) dwarfs the contribution by their vastly more numerous low-mass cousins. These mechanisms can halt accretion onto massive stars and limit star formation in massive star clusters (MSCs), which can host thousands of massive stars. For stellar winds, I discuss how we can use observations to constrain a range of kinetic energy loss channels for the shock-heated gas from stellar winds in MSCs. I demonstrate that the kinetic energy injected by stellar winds in MSCs is not a significant contributor to stellar feedback for young MSCs. I argue instead that radiation pressure is likely the dominant feedback mechanism in massive star and MSC formation. Therefore detailed simulation of their formation requires an accurate treatment of radiation. For this purpose, I have developed a new, highly accurate hybrid radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. With this new method, I performed a suite of three-dimensional radiation-hydrodynamic simulations of the formation of massive stars and MSCs. For individual massive stellar systems, I find that mass is channeled to the massive stellar system via gravitational and Rayleigh-Taylor instabilities. I will also present a simulation of the formation of a MSC from the collapse of a dense, turbulent, magnetized million solar mass molecular cloud. I find that the influence of the magnetic pressure and radiative feedback slows down star formation. These early results suggest that the combined effect of turbulence, magnetic pressure, and radiative feedback from massive stars is responsible for the observed low star formation efficiencies in molecular clouds.
As of last year, the Large Synoptic Survey Telescope (LSST) has begun construction on the summit of Cerro Pachon. As the top-rated flagship for ground-based astronomy in the next decade, LSST will provide an unprecedented dataset of 37 billion objects observed in both space and time. The time domain aspect of LSST is an especially promising source of new discoveries: the main survey is expected to generate new samples of thousands of supernovae, cataclysmic variables, stellar flares, and regular variables, amongst other denizens of the time-domain zoo, each one of which will generate an "alert" within 60 seconds of observation. Sorting amongst these transient and variable objects poses a challenging task: transient events of interest must be identified and prioritized, so that valuable follow-up resources (which are easily saturated by the volume of LSST alerts per night) are deployed on the events with the most potential to provide transformative understanding of particular phenomena. For LSST, this task is of course at a beyond-human scale, requiring sophisticated machine learning algorithms to provide real-time characterization and prioritization. However, another challenge looms under the surface of the approaching flood of data: how can truly novel phenomena be recognized and discovered in large datasets? In this talk, I will discuss methods and applications of finding anomalous data in astronomical datasets. Anomaly identification is a powerful means to both discover novel phenomena, as well as to identify problematic data so that it may be cleaned from the database. Lastly, hunting down anomalies is an exciting way to engage citizen scientists in astronomical discovery, whose efforts have repeatedly demonstrated the power of the crowd in uncovering previously-unnoticed phenomena.
November 2, 2016 | 11:30 AM | ERC 401b | Special Seminar Special Presentation: Seeing the Universe with the X-ray Surveyor Feryal Ozel, University of Arizona
X-ray Surveyor (Lynx) is a NASA flagship mission concept that is developed in preparation for the 2020 Decadal Survey. With a large effective area and a high angular resolution, it will offer an unprecedented sensitivity in X-rays that will enable the studies of baryon cycles in galaxies, the first black holes in the universe, and feedback on all scales. I will describe the developing mission concept and how this X-ray vision will be necessary to get a complete picture of the evolution of the universe.
December 5, 2016 | 12:00 PM | ERC 401 | Special Seminar CMB Lensing: Fundamental Physics from Maps of the Invisible Blake D. Sherwin, UC Berkeley
Dark matter not only forms an invisible cosmic scaffolding within which galaxies form, its distribution in the universe also contains a wealth of information about neutrinos, inflation, and dark energy. Measurements of gravitational lensing in the cosmic microwave background (CMB) allow this matter distribution to be directly seen and mapped out to high redshifts. In my talk, I will discuss current and future work in this new but rapidly advancing field. In particular, I will show new measurements of CMB lensing with the ACTPol experiment and discuss the promise of future ultra-high-precision studies of the lensing signal with the CMB Stage-IV experiment. Lensing is not only a signal, however, but also a source of noise that limits how much we can learn about the early universe via B-mode polarization. In my talk, I will explain why delensing - removing the lensing effect to reveal the primordial sky - is crucial for the future of CMB science, showing recent work in this new area.