Spring 2023 Colloquium Series
The Spring 2023 Joint Astrophysics Colloquium will be held on Tuesdays at 11:00am in the Peyton Hall Auditorium and will be followed by the Bahcall Lunch at 12:30pm in Jadwin Hall.
Please find the spring speaker list below.
| Date | Name and Institution | Title and Abstract |
|---|---|---|
| January 31, 2023 | Dave Stevenson California Institute of Technology |
Mixing and Unmixing in Planets Planets are not layered in general. The strong evidence of layering on Earth arises because the main components (mantle and core) are immiscible. This is a thermodynamic property and nothing to do with gravity. However, immiscible phases can macrosegregate, allowing gravity to place the more dense component at the bottom. Diffusion of the higher molecular weight species is slow and frustrated by convection. However, central concentration of heavy elements can arise in giant planets (including ice giants) because of the way planets are assembled: The densest material is also the material that aggregates first, and hydrogen is accreted on top. In this case, the various constituent parts are miscible (unlike the case of mantle and core on Earth) but separated at birth. In sufficiently massive "SuperEarths", there should be no core and mantle because entropy wins. I will discuss our current understanding of the imperfect separation of core from mantle on Earth and the extent to which a compositional gradient in giant planets may be legacy of formation. |
| February 7, 2023 | Martin Lemoine Institut d'Astrophysique de Paris |
Particle acceleration in astrophysical, magnetized turbulent plasmas How magnetized turbulent plasmas can accelerate charged particles to high energies represents a long-standing question with far-reaching implications for high-energy and multi-messenger astrophysics. It indeed goes back to the seminal works of Enrico Fermi (1949, 1954) and nowadays, it is commonly invoked to model the generation of non-thermal particle spectra in a broad variety of astrophysical sites, including extreme, relativistic sources. In particular, it has recently been considered as a possible origin for the high-energy neutrinos seen by Ice Cube in the direction of nearby active galactic nuclei. |
| February 14, 2023 | William H. Matthaeus University of Delaware |
Turbulence in collisionless space plasma: the Big Picture Turbulence is a near ubiquitous feature of fluids and plasmas in geospace, the heliosphere and in astrophysics and well as in laboratory plasma and in the terrestrial environment. Turbulence links large scale energy reservoirs with small scale dissipation processes. Consequently, it is responsible for many features of space plasmas including heating, charged particle scattering and energy transport across wide ranges of spatial scale and location. This account of the Big Picture of space turbulence starts with the likely energy sources that powers the heating and acceleration of the solar wind. What follows is a progression of cross scale couplings that are described in adaptations of classical turbulence theory. At energy containing scales, von Karman similarity provides a top-down description of energy decay. The von Karman picture is demonstrated using solar wind spacecraft data near earth. At smaller scales a several decade inertial range is present the solar wind. Energy transfer through this cross scale conduit is described using three methods: phenomenology, Yaglom-Kolmogorov third order law, and scale filtering. Transfer through the inertial range generates small scale structures, or intermittency, in which kinetic processes are concentrated. Finally, the kinetic dissipation itself, defined as conversion of fluid scale energy into internal energy, is accomplished though the pressure-work and the pressure strain interaction. These are quantified in some detail due to recent advances in both kinetic plasma simulation, and capable multispacecraft measurements. The cross scale couplings discussed here span scales from the large energy reservoirs to kinetic scale dissipation and are illustrated using spacecraft missions including STEREO, ACE, Helios, Voyager, Parker Solar Probe, Cluster and Magnetosphere Multiscale. The presentation concludes with outstanding questions will be addressed by new missions such as Helioswarm and PUNCH. |
| February 21, 2023 | Christoph Pfrommer Leibniz-Institute for Astrophysics Potsdam |
Cosmic ray feedback and magnetic dynamos in galaxy formation Understanding the physics of galaxy formation is an outstanding problem in modern astrophysics. Recent cosmological simulations have demonstrated that feedback by star formation, supernovae and active galactic nuclei appears to be critical in obtaining realistic disk galaxies and to slow down star formation to the small observed rates. However the particular physical processes underlying these feedback processes still remain elusive. In particular, many of these simulations neglected magnetic fields and relativistic particle populations (so-called cosmic rays). Those are known to provide a pressure support comparable to the thermal gas in our Galaxy and couple dynamically and thermally to the gas, which seriously questions their neglect. After introducing the underlying physical concepts, I will present our recent efforts to model cosmic ray physics and magnetic fields in galaxy formation. In particular, I will explain how cosmic rays interact with and propagate through the magnetized plasma in the interstellar and circumgalactic media and how we can observationally test these theoretical considerations using new high-sensitivity MeerKAT observations. I will then demonstrate that cosmic rays play a decisive role in the formation and evolution of spiral galaxies by providing feedback that regulates star formation and drives gas out in galactic winds. Comparing cosmic ray spectra of electrons and protons to observational data and studying the correlation of the far-infrared emission with the gamma-ray and radio emission from galaxies enables us to test the cosmic ray feedback and dynamo models for the growth of galactic magnetic fields. This argues that a complete understanding of galaxy formation necessarily includes these non-thermal components. |
| February 28, 2023 | Kiyoshi Masui Massachusetts Institute of Technology |
A Synoptic View of Fast Radio Bursts with CHIME For more than a decade, enigmatic extragalactic flashes called fast radio bursts (FRBs) have defied a definitive explanation for their origin. In addition, the unique properties of FRBs make them promising probes of both cosmology and the distribution of gas on intergalactic scales. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is the only radio telescope capable of instantaneously observing hundreds of square degrees with the sensitivity of a 100-meter scale aperture. As a result, its transient search instrument, CHIME/FRB, has detected thousands of FRBs, increasing the known sample by an order of magnitude. I will give an overview of CHIME/FRB's most recent results, where observations of particular sources and statistical analyses of the FRB population are starting to reveal the nature of this mysterious phenomenon. I will then describe an effort to augment CHIME/FRB's capabilities by adding Outrigger telescopes, which will be located across North America and will precisely localize FRB sources using very long baseline interferometry. The resulting large sample of localized FRBs will allow for detailed measurements of the large-scale distribution of baryons in the universe, providing precise constraints on feedback processes in galaxy evolution. |
| March 7, 2023 | Gwen Rudie Carnegie Observatories |
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| March 14, 2023 | Break | |
| March 21, 2023 | Colin Hill Columbia University |
Searching for Cosmological Concordance with New Physics in the Dark I will discuss recent and ongoing work focused on attempts to restore concordance amongst cosmological data sets, motivated by discrepancies amongst some inferences of the cosmic expansion rate (H_0) and the matter clustering amplitude (S_8). I will explain why the most viable models to resolve the H_0 problem invoke new physics at or prior to the last scattering epoch. Such models include modified recombination scenarios, quasi-accelerating early dark energy (EDE) models (and extensions thereof, featuring EDE-dark matter interactions), or scenarios featuring new light particles with non-trivial interactions. I will present constraints on such scenarios derived using data from the Atacama Cosmology Telescope (ACT), the Planck satellite, and large-scale structure surveys. I will highlight newly obtained constraints on EDE models derived from Lyman-alpha forest data, which severely hinder the ability of this scenario to resolve the H_0 problem. I will conclude with a look ahead to forthcoming CMB analyses from ACT, which will provide a powerful test of these scenarios in the low-noise, high-resolution regime. |
| March 28, 2023 | Heather Knutson California Institute of Technology |
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| April 4, 2023 | Nadine Neumayer Max Planck Institute for Astronomy |
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| April 11, 2023 | Ting Li University of Toronto |
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| April 18, 2023 | Avishay Gal-Yam Weizmann Institute of Science |
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| April 25, 2023 | Nia Imara University of California Santa Cruz |
IAS/PU Colloquia Fall 2022
The Fall 2022 Joint Astrophysics Colloquium will be held on Tuesdays at 11AM and will be followed by the Bahcall Lunch at 12:30.
Please find the speaker schedule below. Videos on IAS website: https://www.ias.edu/video-tags/iaspu-joint-astrophysics-colloquium
| Date | Name | Title |
|---|---|---|
| September 6, 2022 | Mark Devlin University of Pennsylvania |
Large-Scale Millimeter Wave Surveys Millimeter-wave surveys of the sky have the potential for yielding a wealth of information about our universe from the first instants of its existence to our own solar system. I will describe how modern measurements of the cosmic microwave background (CMB) are being used to measure how our universe has evolved over cosmic time leading to a better understand the fundamental parameters governing its nature. I will present recent results from the Atacama Cosmology Telescope (ACT) and future plans for the Simons Observatory program. |
| September 13, 2022 | Robin Canup SWRI, Boulder |
Origin of the Moon: New Results and Open Issues A primary scientific outcome of the Apollo program was the giant impact theory for lunar origin, in which a collision at the end of Earth’s main accretionary phase creates a disk from which the Moon forms. In the past decade, the nature of a Moon-forming impact has become highly debated, driven by increasingly precise sample analyses that show that the Earth and Moon have essentially identical isotopic compositions across all non-volatile elements. Giant impacts usually produce disks that originate primarily from the impactor (“Theia”) rather than from the target protoearth. Meteorites that originate from Mars, and nearly all those from parent bodies in the asteroid belt, have quite different isotopic compositions than the Earth. If Theia had been similarly non-Earth like, and the pre-lunar disk originated primarily from Theia, one would then most naturally expect measurable differences between the Earth and Moon. Instead, they are indistinguishable across most elements. Many new scenarios have been proposed to resolve this fundamental dilemma, involving different Theia compositions, protolunar disk evolutions, and/or early Earth-Moon dynamical histories. I will discuss several of these, as well as key remaining uncertainties and prospects for relevant new constraints from future lunar exploration. |
| September 20, 2022 | Deirdre Shoemaker University of Texas at Austin |
Brave New World of Numerical Relativity After decades of preparation, the era of gravitational wave astronomy has begun. The gravitational wave detectors, LIGO and Virgo, have published a catalog of 90 events of coalescing compact objects including black holes and neutron stars. I will present the role that numerical relativity played in the unveiling of the gravitational wave sky and anticipate how it might improve our understanding of gravity as the detectors improve. |
| September 27, 2022 | Kaitlin Kratter University of Arizona |
A Continuous Theory of Stellar System Formation A satisfying theory for star or planet formation should not consider these processes in isolation. With the power of recent observational surveys, we are well positioned to test detailed theoretical models of multiple-star formation and orbital evolution across diverse galactic environments. Simultaneously we can begin to couple our understanding of the earliest phases of star formation with the onset of planetary system formation. I will review current theoretical and observational progress on multiple star formation, and highlight areas of continued uncertainty. |
| October 4, 2022 | Alex Schekochihin University of Oxford |
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| October 11, 2022 | Frank van den Bosch Yale University |
New Insight into Cosmology and the Galaxy-Halo Connection from Non-Linear Scales |
| October 18, 2022 | Fall Break- No Colloquium | |
| October 25, 2022 | Jo Bovy University of Toronto |
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| November 1, 2022 | Ben Shappee IfA, Hawaii |
The All-Sky Automated Survey for Supernovae (ASAS-SN) For the first time, the entire visible sky is being surveyed for the violent, variable, and transient events that shape our universe by the All-Sky Automated Survey for Supernovae (ASAS-SN). Combined, ASAS-SN, Asteroid Terrestrial-impact Last Alert System (ATLAS), The Zwicky Transient Facility (ZTF), the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), Gaia, and the Transiting Exoplanet Survey Satellite (TESS) now monitor the whole sky, at high cadence with a combined total of 32 telescopes distributed at 9 sites around and above the world. Each survey has a different cadence and depth. I will briefly review major ongoing transient surveys, contrasting their capabilities and goals. I will then use a handful of recent discoveries to highlight opportunities that these new capabilities present. I will focus on multi-messenger astronomy (with LIGO and IceCube); high-cadence, high-precision observations (with Kelper, TESS, and POISE); and the remarkable repeating partial tidal disruption event ASASSN-14ko. I will reflect on the challenges the field will face both now and in the LSST-era. Finally, I will end by describing new and future ways we are making ASAS-SN an even more useful tool for the entire community and introduce the Spectral Classification of Astronomical Transients (SCAT) survey on the UH 2.2m telescope, a new survey that will rapidly trigger on, observe, and classify publicly announced transients fully-automatically without the need for human intervention. |
| November 8, 2022 | Dimitrios Psaltis University of Arizona |
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| November 15, 2022 | Samaya Nissanke University of Amsterdam |
First detection of an isolated black hole, and mass measurement of isolated white dwarfs through astrometric microlensing
We recently detected an isolated stellar-mass black hole (BH) unambiguously for the first time, and measured its mass, distance and velocity. We used HST to carry out precise astrometry of the source star of the long-duration, high-magnification microlensing event OGLE-11-462. Combining HST astrometry, OGLE photometry, and spectroscopic measurements, we obtain a lens mass of ~7 solar mass and a distance of ~1.6 kpc. The lens emits no detectable light, which confirms its BH nature. Its proper motion is offset from the mean motion of Galactic-disk stars at similar distances by ~45 km/s, suggesting that the BH received a natal kick from its supernova explosion. In a reprise of the famous 1919 solar-eclipse experiment that confirmed Einstein's general relativity, the nearby white dwarf Stein 2051b passed very close to a 19th magnitude background star. As it passed in front, Stein 2051B caused a deflection of the background star's image by ~2 milliarcsec, which we observed with HST. This allowed us to determine the mass of Stein 2051 B using this technique of astrometric microlensing for the first time outside the solar system. We have measured masses of 2 WDs through this technique, and our measurements lend support to the white-dwarf evolutionary theory. |
| November 22, 2022 | Dominika Wylezalek University of Heidelberg |
Multiphase and multi-scale AGN feedback processes AGN feedback is now widely considered to be one of the main drivers in regulating the growth of massive galaxies. In my talk I will describe several efforts in our group to understand the power, reach and impact of AGN feedback processes. We find significant evidence for AGN feedback signatures even in low-luminosity AGN and we are now using molecular gas as a tracer to investigate if and how feedback may impact and quench galaxies at low redshift. At higher redshift, it appears that AGN-driven outflows can indeed suppress star formation in their hosts, consistent with the AGN having a negative impact on galaxy evolution. However, both star formation and quasar activity peak at z ~ 2-3 where AGN are expected to impact the build-up of stellar mass the most and I will present recent efforts in our group to characterise feedback processes in powerful AGN on CGM scales at and near Cosmic Noon. In particular, our team recently discovered a unique population of luminous high-z quasars (ERQs) with extreme outflow properties. At the same time, more and more exotic AGN populations with extreme signatures are being discovered at that redshift. These populations are ideal to obtain a census of the overall mass and energy budget of both outflow and infall/feeding from the CGM, an essential requirement to probe the detailed and full feedback loop. Finally, I will also introduce the JWST ERS Program Q3D which studies the impact of three carefully selected luminous quasars on their hosts. Our program will serve as a pathfinder for JWST science investigations in IFU mode. Depending on JWST's science schedule, I may show some of the very first JWST science results. |
| November 29, 2022 | Lisa Kewley CfA, Harvard & Smithsonian |
Joint IAS Princeton University Astrophysics Colloquium - (not open to the public)
Spring 2022 Colloquium Speakers (not open to the public)
Spring 2022 Colloquium Series
The Spring 2022 Joint Astrophysics Colloquium will be held on Tuesdays at 11:00am and will be followed by the Bahcall Lunch at 12:30.
Please find the spring speaker list and links to videos below.
| Date | Name | Title |
| January 25, 2022 |
Lía Corrales (Virtual) |
New Frontiers of Short Wavelength Exploration: From Astromineralogy to Exoplanet Uncovering the physics of galaxy evolution has been a longstanding problem for astronomers. Physical galaxy properties like the star formation rate, stellar mass, and metallicity can tell us not only how these properties change over generations of galaxies, but they also give us a window into the conditions of the universe at the time of galaxy formation. Galaxy surveys, which are predominantly used to measure these properties, only observe the brightest galaxies, which are a biased sample. Line intensity mapping (LIM) observes the aggregate emission from brighter and fainter galaxies over much larger volumes. The EXCLAIM survey is a pathfinder for this technique, and has the potential to aid in constructing a full census of galaxy emission while minimizing sample variance. In this talk I will present how we can use LIM surveys to construct a galaxy property census. Specifically, I will discuss currently planned methods using LIM to uncover galaxy properties like molecular hydrogen density, star formation, and metallicity properties, as well as their limitations. I will also discuss potential ways we could get around these hurdles using hydrodynamic simulations along with semi-analytic star formation models. Finally we will discuss how these methods could be applied to EXCLAIM and other upcoming LIM surveys. |
| February 1, 2022 | Anthony Pullen (Virtual) NYU |
A Galaxy Property Census with Line Intensity Mapping Uncovering the physics of galaxy evolution has been a longstanding problem for astronomers. Physical galaxy properties like the star formation rate, stellar mass, and metallicity can tell us not only how these properties change over generations of galaxies, but they also give us a window into the conditions of the universe at the time of galaxy formation. Galaxy surveys, which are predominantly used to measure these properties, only observe the brightest galaxies, which are a biased sample. Line intensity mapping (LIM) observes the aggregate emission from brighter and fainter galaxies over much larger volumes. The EXCLAIM survey is a pathfinder for this technique, and has the potential to aid in constructing a full census of galaxy emission while minimizing sample variance. In this talk I will present how we can use LIM surveys to construct a galaxy property census. Specifically, I will discuss currently planned methods using LIM to uncover galaxy properties like molecular hydrogen density, star formation, and metallicity properties, as well as their limitations. I will also discuss potential ways we could get around these hurdles using hydrodynamic simulations along with semi-analytic star formation models. Finally we will discuss how these methods could be applied to EXCLAIM and other upcoming LIM surveys. |
| February 8, 2022 | Stephon Alexander Brown |
The Chiral Universe Among a handful of mysteries in the LambdaCDM paradigm of cosmology, I focus on three: Dark Matter, Baryogenesis and the origin of structure. I then provide a pedagogical introduction to Chiral Gravity and show how these three mysteries may be interconnected. I also discuss some observational windows including the inevitability of Superfluid Dark matter. |
| February 15, 2022 | Shirley Ho Flatiron Institute |
Learning Symbolic Equations with Deep Learning We develop a general approach to "interpret" what a network has learned by introducing strong inductive biases. In particular, we focus on Graph Neural Networks. The technique works as follows: we first encourage sparse latent representations when we train a GNN in a supervised setting, then we apply symbolic regression to components of the learned model to extract explicit physical relations. The symbolic expressions extracted from the GNN using our technique also generalized to out-of-distribution data better than the GNN itself. Our approach offers alternative directions for interpreting neural networks and discovering novel physical principles from the representations they learn. In particular, we will show examples of recovery of newton's law and masses of solar system bodies with real ephemeris data and recovery of navier-stokes equations with turbulence dataset. We will speculate what one can do with this new tool. |
| February 22, 2022 | Elisabete M. de Gouveia Dal Pino University of São Paulo |
Cosmic Ray Acceleration by Magnetic Reconnection: Probing Extreme Energies and the Origin of Gamma-Ray and Neutrino Emission from Black Holes and Relativistic Jets of Active Galaxies View presentation here. Relativistic Jets emanating from Black Holes (BH) of active galaxies are believed to be among the most extreme particle accelerators and very high energy (VHE) emitters in the universe. Only lately, combining theory, numerical simulations and observations, we have started to understand the potential physical processes that prevail in the surrounds of these BHs in order to explain major puzzles like the origin of the VHE gamma-ray flares and ultra-high-energy cosmic rays (UHECRs). In those inner regions, magnetic fields are dynamically dominating and particle acceleration driven by magnetic reconnection is expected. In this talk, I will discuss particle acceleration by magnetic reconnection in turbulent flows and present recent results that combine three-dimensional global magnetohydrodynamic relativistic simulations with the injection of test particles, showing how particles can be stochastically accelerated in the relativistic jets and the accretion flows around BHs by magnetic reconnection up to ultra-high energies. Finally, I will show that these accelerated particles could explain the gamma-ray flares and associated neutrino emission observed in these sources. |
| March 1, 2022 | Suvrath Mahadevan Penn State |
Pathways to Earth-Mass Planets with Precision Spectroscopy Modern astronomical spectrometers are approaching the exquisite sensitivity to detect the signature of an Earth-mass planet around stars like the Sun. I shall discuss the challenges involved in making these difficult measurements with the Doppler radial velocity technique, and the evolution of the design of these instruments as they seek ever-tighter control of environmental parameters, and increased measurement precision. A suite of new technologies like frequency stabilized laser combs, low drift etalons, and deeper understanding of the detectors is enabling a new level of precision in radial velocity measurements - as well as illustrating new challenges. I will use two such instruments we have built to illustrate some of the underlying physics and measurement challenges. I will then discuss how the stars themselves are the remaining challenge, as magnetically driven processes create ‘stellar activity’ noise that can masquerade as planets and obfuscate their detection. I shall highlight a few paths we are exploring to mitigate this – using our star, the Sun, as a guide, and discuss whether the goal of discovering and characterizing terrestrial mass planets capable of hosting liquid water on their surfaces is now within reach. |
| March 15, 2022 | James Lowenthal Smith College |
Satellite Swarms vs. Astronomy and the Night Sky View presentation here. |
| March 22, 2022 | Eduardo Bañados MPIA |
The birth of the first massive galaxies and black holes We are the first generation of human beings able to directly observe and study the cosmic era when the first galaxies and black holes formed. Quasars are among the most luminous sources known and can be studied in detail even during the first billion years of the Universe (at redshifts z>6). I will summarize my team's efforts to search for and characterize the most distant quasars. This has led to the discovery of the largest number of bright quasars at z>6, including the most distant radio-source known at z~7, and the three most distant quasars known at z>7.5. These distant quasars provide important clues about the build-up of the first massive galaxies and black holes, as well as the epoch of reionization. I will review the diverse range of physical properties of these quasars on different scales, including follow-up studies from X-rays to radio wavelengths. |
| March 29, 2022 | Christopher Reynolds IoA Cambridge |
Searching for axion-like particles with X-ray observations of galaxy clusters. View presentation here. There has been a surge of interest within the particle-physics and dark matter communities in axions and axion-like particles (ALPs). These particles result from a possible extensions to the Standard Model that may solve the Strong-CP problem, and are further motivated by String Theory. Galaxy clusters are a superb laboratories for exploring ALP physics. Clusters are permeated by a magnetized hot intracluster medium (ICM) that can efficiently interconvert photons and ALPs. Here, I discuss how the transparency (or lack thereof) of the ICM to X-rays becomes a powerful way to constrain ALPs. I show that a careful examination of X-ray observations of cluster-hosted active galactic nuclei (AGN) by the Chandra X-ray Observatory allow the tightest constraints to date on ALP/photon coupling of ALPs in the low-mass regime (ALP masses less than ~peV). I finish by discussing the future prospects of these studies with the next generation X-ray observatories. |
| April 5, 2022 | Sabrina Stierwalt Occidental College |
The Baryon Cycle in Dwarf-Dwarf Mergers: Fueling Hierarchical Assembly Both cosmological simulations and observations of the ultraviolet luminosity function suggest dwarf galaxies are the dominant population at high redshifts and that the galaxy merger rate per unit volume is dominated by low mass galaxies. However, dwarf-dwarf interactions have not yet been subject to systematic study, even in the nearby universe. I will report on our efforts to do just that: TiNy Titans is the first systematic study of a sample of isolated interacting dwarf galaxies and the mechanisms governing their star formation. How much of what we know about massive galaxy mergers - triggering of starbursts, significant rearranging of gas & dust, AGN growth - occur in the shallower gravitational potential wells of dwarf galaxies? Do we observe these low mass mergers at the rate predicted by cosmological simulations? Do groups of only dwarf galaxies exist? I will also highlight our most recent results investigating the age and mass distributions of the star cluster populations in dwarf mergers as observed with high resolution Hubble imaging. |
| April 12, 2022 | Suvi Gezari STScI |
The Wild West of Nuclear Transients Central massive black holes will reveal themselves in a galaxy when they flicker and flare as they feed on gas and stars. We are conducting a systematic study of nuclear transients in the Zwicky Transient Facility alert stream, and have assembled the largest ever sample of tidal disruption events (TDEs), as well as revealed new extreme populations of flaring and "changing look" AGN. TDEs provide a rare glimpse of dormant massive black holes lurking in the centers of galaxies, and their luminous outbursts of radiation are valuable probes of accretion physics, jet formation, and the circumnuclear environment and stellar population. The growing census of TDE discoveries, with hundreds more on the horizon with the start of the Vera C. Rubin Observatory Legacy Survey of Space and Time, are enabling us to do population studies of TDEs for the first time. I will present exciting new developments in our understanding of the physical conditions driving the light curves, broadband spectral energy distributions, and spectroscopic sub-classes in TDEs, and how they relate to the properties of their host galaxies and the masses of their central supermassive black holes. |
| April 19, 2022 | Hilke Schlichting UCLA |
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| April 26, 2022 | Andrea Ghez UCLA |
From a Possibility to a Certainty of a Supermassive Black Hole Learn about new developments in the study of supermassive black holes. Through the capture and analysis of twenty years of high-resolution imaging, the UCLA Galactic Center Group has moved the case for a supermassive black hole at the center of our galaxy from a possibility to a certainty and provided the best evidence to date for the existence of these truly exotic objects. This was made possible with the first measurements of stellar orbits around a galactic nucleus. Further advances in state-of-the-art of high-resolution imaging technology on the world’s largest telescopes have greatly expanded the power of using stellar orbits to study black holes. Recent observations have revealed an environment around the black hole that is quite unexpected (young stars where there should be none; a lack of old stars where there should be many; and a puzzling new class of objects). Continued measurements of the motions of stars have solved many of the puzzles posed by these perplexing populations of stars. This work is providing insight into how black holes grow and the role that they play in regulating the growth of their host galaxies. Measurements this past year of stellar orbits at the Galactic Center have provided new insight on how gravity works near a supermassive hole, a new and unexplored regime for this fundamental force of nature. |
Fall 2021 Colloquium Series
The Fall 2021 Joint Astrophysics Colloquium will be held on Tuesdays at 11AM and will be followed by the Bahcall Lunch at 12:30.
Please find the Fall speaker schedule at this link and below. Videos on IAS website: https://www.ias.edu/video-tags/iaspu-joint-astrophysics-colloquium
| Date | Name | Title (link to videos of talks is here.) |
|---|---|---|
| Sep 7 11:00am | Romain Teyssier | Cosmic magnetism from a computational perspective |
| Sep 14 11:00am | Alice Quillen | Soft Astronomy |
| Sep 21 11:00am | Amina Helmi | New views on the Milky Way |
| Sep 28 11:00am | Uros Seljuk | All you need is a Normalizing Flow |
| Oct 5 11:00am | Brett McGuire | The PAH Revolution: Cold, Dark Carbon at the Earliest Stages of Star Formation |
| Oct 12 11:00am | Jennifer Lotz | Gemini Observatory in the 2020's |
| Oct 26 11:00am | Ellen Zweibel | TBA |
| Nov 2 11:00am | Xuening Bai | TBA |
| Nov 9 11:00am | Kenta Kiuchi | TBA |
| Nov 16 11:00am | Sera Markoff | TBA |
| Nov 23 11:00am | Alexandra Amon | TBA |
| Nov 30 11:00am | Bethany Ehlmann | TBA |
2021 Summer Colloquium Series
The 2021 Summer Colloquium Series led by Professor Eliot Quataert begins virtually on
Wed. Jul 21, at 12:00PM, and continues on Tuesdays 7/27 through 8/24 at 12:30PM.
The list of speakers, talk titles and select colloquium recording links appear below. Zoom link will be sent by email.
| Date | Name | Title (Video Link to Talk) |
|---|---|---|
| July 21, 2021 12:00PM |
Alice Pisani Princeton |
Unraveling The Universe With Cosmic Voids Modern surveys provide access to high-quality measurements on large areas of the sky, sampling the galaxy distribution in detail also in the emptiest regions, voids. Void cosmology is becoming an increasingly active sector of galaxy clustering analysis: by measuring void properties, such as density profiles or void number counts, it is possible to constrain cosmological parameters. Cosmic voids are particularly sensitive to the properties of dark energy and neutrinos, and are a powerful tool to test modifications of the laws of general relativity. Studying voids provides a novel perspective to unravel the unsolved mysteries of our Universe. In this talk I introduce cosmic voids as a tool for cosmology, I present recent results—with a particular focus on the advantages of calibration-free approaches—and I discuss future developments in the field. |
| July 27, 2021 12:30PM |
Kirk Barrow Stanford | High-Cadence Synthetic Observations and Neural Networks in the Era of JWST As astronomers near the commissioning of the extremely large telescopes, the Rubin Observatory, as well as new space-based observatories like the Roman Space Telescope and JWST to peer more deeply into our Universe, our community is challenged to develop a theoretical and modeling framework to characterize and study what will be humanity's greatest astronomical discoveries. My research addresses this need by generating detailed, state-of-the-art synthetic observations from hydrodynamic cosmological simulations. By calculating all the processes that photons undergo as they travel across the Universe from the surface of a distant star to a telescope’s detector, my collaborators and I have been able to disentangle perplexing trends in observed galactic spectra as well as make predictions for what we might unveil in the near future. Topics we have investigated in prior work include massive black hole formation, the first stars and galaxies, and the intricate interplay between nebular emission lines and the escape fraction of ionizing radiation. Looking forward, I propose to create the largest and most detailed database of synthetic observational tools and predictions at a time that will come to define astronomy for generations. |
| Aug. 3, 2021 12:30PM |
Diana Powell UCSC |
Microphysical Insights into Protoplanetary Disks and Exoplanet Atmospheres A fundamental understanding of planetary histories and characteristics requires an empirical connection between planet formation and evolved planets—a long-sought goal of astrophysics. This connection is now increasingly possible due to simultaneous revolutions in the observations of protoplanetary disks and exoplanet atmospheres. A key step towards relating these observations of different evolutionary stages is to characterize the composition of material in protoplanetary disks and relate these properties to the atmospheric composition of planets. In this talk, I will discuss initial steps that I have taken towards this goal. I will provide evidence that protoplanetary disks are more than an order of magnitude more massive than previously appreciated, that the detailed properties of clouds shape observations of substellar atmospheres, and that the physics of modeling clouds gives a new understanding of the compositional distribution in protoplanetary disks. I will conclude by briefly discussing avenues for relating planetary properties to the mass inventory in protoplanetary disks in order to develop the observationally-validated framework required to compositionally relate evolved planets to planet formation. |
| Aug. 10, 2021 12:30PM |
Joey Rodriguez Michigan State |
Understanding Planetary Evolution with Eclipsing Disks & Transiting Planets The success of ground-based transit and RV surveys, and the Kepler/K2 and TESS missions, have shifted the exoplanet field from pure discovery to a combination of discovery, demographic analysis, and detailed characterization, especially for exoplanet atmospheres. We are using data from the TESS, Kepler/K2, and ground-based transit surveys to find keystone planetary systems around bright stars (those well suited for atmospheric observations) that can help address specific questions about planet formation and evolution. We are also studying the birthplaces of planets by searching for occultations of newly formed stars by their protoplanetary disks. These systems provide insight into the conditions required for planet formation. I will describe our recent results from both projects and discuss how we will study these types of objects in future surveys. |
| Aug. 24, 2021 12:30PM |
Vladimir Zhdankin Princeton |
First-Principles Modeling of Kinetic Turbulence in High-Energy Astrophysical Plasmas Kinetic plasma physics is an integral, but often neglected, component of many high-energy astrophysical systems. Understanding the dynamics and energization processes in collisionless plasmas is essential for interpreting the observable radiation spectra, luminosities, and variability of systems such as pulsar wind nebulae, accretion flows onto compact objects, and relativistic jets from active galactic nuclei. Kinetic turbulence has long been proposed as a primary process for energizing these collisionless plasmas, but questions remain as to its viability for producing nonthermal particle populations in various physical regimes. Particle-in-cell (PIC) simulations have recently opened this rich topic to detailed, first-principles numerical and theoretical scrutiny. I will overview recent progress on understanding particle energization in relativistic (and trans-relativistic) plasma turbulence, spurred by PIC simulations, including the demonstration of phenomena such as nonthermal particle acceleration, electron-ion thermal decoupling, and intermittent beaming of radiation. These new insights have applications for modeling various high-energy astrophysical systems. |
2021 Spring Colloquium Series
The Spring 2021 Joint Astrophysics Colloquium was held virtually on Tuesdays at 11AM and was followed by the virtual Bahcall Lunch at 12:30.
| Date | Name | Title (Video Link to Talk) (pvt) |
|---|---|---|
| Feb. 2, 2021 | Eliot Quataert Princeton |
The Impact of Cosmic-Rays on Galaxy Formation Relativistic cosmic-rays created by stellar and black hole feedback may play an important role in many aspects of structure formation. Cosmic-rays can drive outflows from star forming galaxies and heat diffuse gas in the circumgalactic and intergalactic medium. In this talk I will describe some of the possible impact(s) of cosmic-rays on galaxy formation, observational probes of their impact, and the theortical uncertainities in our understanding of the role of cosmic rays in structure formation. |
| Feb. 9, 2021 | Feryal Özel University of Arizona |
Black Hole Physics at the Horizon Scale Recent observational advances with the Event Horizon Telescope, GRAVITY, and LIGO/VIRGO have opened up new avenues for studying black hole physics at horizon scales. In this talk, I will discuss what we have learned about the spacetimes of astrophysical black holes and how strong-field gravity is imprinted on their images. I will also present how the observations help us model and understand the heating and acceleration of plasmas on horizon scales. |
| Feb. 16, 2021 | Sherry Suyu Max Planck Institute for Astrophysics |
Cosmology with Gravitational Lens Time Delays Strong gravitational lenses with measured time delays between the multiple images can be used to determine the Hubble constant (H0) that sets the expansion rate of the Universe. An independent determination of H0 is important to ascertain the possible need of new physics beyond the standard cosmological model, given the tension in current H0 measurements. I will describe techniques for measuring H0 from lensing with a realistic account of systematic uncertainties, and present the latest results from a program aimed to measure H0 from lensing. Search is underway to find new lenses in imaging surveys. An exciting discovery of the first strongly lensed supernova offered a rare opportunity to perform a true blind test of our modeling techniques. I will show the bright prospects of gravitational lens time delays as an independent and competitive cosmological probe. |
| Feb. 23, 2021 | Jørgen Christensen-Dalsgaard Aarhus University |
Probing red giants with Kepler The frequencies of oscillations observed on a stellar surface carry information about the properties of the stellar interior. Asteroseismology, i.e., the unravelling of this information, has made a huge leap thanks to the photometric observations obtained with NASA' Kepler mission, launched in 2009 to search for planets around other stars. In my talk I focus on the study of red-giant stars, showing a broad range of oscillations, probing both the outer parts and the deep core of the stars. Amongst other remarkable results, this has allowed distinguishing stars according to their nuclear energy source and provided detailed information about the properties of internal rotation in these late stages of stellar evolution. |
| Mar. 2, 2021 12:30pm |
Jennifer van Saders University of Hawaii |
Making Sense of Stellar Rotation in Low Mass Stars Stellar rotation carries a wealth of information about stellar populations. In particular, the technique of gyrochronology was developed to utilize the spin-down of stars as a function of time as an indicator of stellar age. Gyrochronology has the potential to yield precise ages for large samples of stars, providing unprecedented chronological information for studies of the Milky Way and extrasolar planets. However, the technique is in its adolescence: it has been tested and validated under limited scenarios, but its weaknesses and limitations have hitherto been largely unexplored. With time-domain data we can address these gaps: we now have access to datasets of rotation periods for tens of thousands of stars, as well as independent asteroseismic ages and rotation periods for a few hundred old (main sequence) stars. I will discuss my comparisons of theoretical rotation models to these data, which have yielded unexpected insights into the rotational and magnetic lives of stars (and the Sun!), as well as a better understanding of the power and peril of gyrochronology as a tool. |
| Mar. 16, 2021 | Brian Nord University of Chicago / Fermilab |
From Galaxies to Faces: Recognizing the Implications of Artificial Intelligence in Astronomy and Society Artificial Intelligence (AI) refers to a set of techniques that rely primarily on the data itself for the construction of a quantitative model. AI has arguably been in development for three quarters of a century, but there has been a recent resurgence in research and application. This current (third) wave of AI progress is marked by extraordinary results --- for example, in image analysis, language translation, and machine automation. Despite the aforementioned modest definition of AI, its potential to disrupt technologies, economies, and society is often presented as (nearly) unmatched in modern times, due in part to the versatility of the algorithms in modeling a wide variety of data. Similarly, there is great promise for applications across the sciences --- for example, simulations, image classification, and automated experimentation --- which are currently being investigated by researchers across the globe. Along with the significant promise of AI, comes great peril: in societal contexts, the consequences include enhanced surveillance, facial recognition, and automated weaponry. In science contexts, the issues are also significant and in many cases related --- for example, bias, lack of uncertainty quantification, and misuse. To take full advantage of the opportunities for AI to accelerate science and improve society, it's essential that we carefully guide its development. During this presentation, we will explore modern AI techniques, like neural networks, and review how they are being developed and deployed in astronomy. Then, we’ll discuss ideas for the future usage of AI in science, including technical barriers for long-term application. Finally, we’ll discuss the roles of scientists and academic communities in the development of AI algorithms |
| Mar. 23, 2021 | Julia Roman-Duval Space Telescope Science Institute |
The Nearby Universe - A Laboratory to Study the Cosmic Build-up of Dust and Metals in Galaxies A key component of the baryon cycle in galaxies is the cycle of metals between the gas and the dust phases in the neutral interstellar medium (ISM). How this cycle depends on environment (in particular metallicity and density) has important implications for how accurately we can trace the chemical enrichment of the universe over cosmic times; either by using dust emission in the far-infrared as a tracer of the ISM in galaxies at high and low redshift; or by using spectroscopy of damped Lyman-alpha systems (DLAs) to measure chemical abundances in neutral gas over a wide range of redshifts. Variations of the abundance and properties of dust within and between galaxies furthermore profoundly affects their evolution, given the key role that dust plays in the chemistry, radiative transfer, and thermodynamics of galaxies. In this talk, I will present results from several independent observational efforts to characterize the dust abundance (dust-to-gas and dust-to-metal ratios) in the Magellanic Clouds and other nearby low-metallicity galaxies, using emission-based tracers of the interstellar medium (FIR, HI 21 cm, CO rotational emission) to map their dust and gas content on the one hand; and using UV absorption spectroscopy with Hubble to directly count metals in the gas phase on the other hand. Both types of studies demonstrate significant variations of the dust abundance with density (within galaxies) and metallicity (between galaxies), which have important implications for the sub-grid physics of galaxy evolution. Surprising patterns in the gas-phase abundances were found from the Hubble spectroscopy, and an interesting tension between the emission-based and absorption-based measurements remains unexplained. |
| Mar. 30, 2021 | Anna Watts University of Amsterdam |
A NICER view of neutron stars NICER, the Neutron Star Interior Composition Explorer, is an X-ray telescope that was installed on the International Space Station in 2017. Its mission is to study the nature of the densest matter in the Universe, found in the cores of neutron stars. NICER uses Pulse Profile Modeling, a technique that exploits relativistic effects on X-rays emitted from the hot magnetic polar caps of millisecond pulsars. The technique also lets us map the hot emitting regions, which form as magnetospheric particles slam into the stellar surface. I will present NICER's current results and ongoing analysis, and discuss the implications for our understanding of ultradense matter, pulsar emission, and stellar magnetic fields. |
| Apr. 6, 2021 | Zhaohuan Zhu University of Nevada, Las Vegas |
Protoplanetary Disk Structure and Young Planet Population Recent ground based observations at various wavelengths reveal a variety of protoplanetary disk structures. These disk structures may help us to constrain the planet formation process. I will first discuss how to apply the planet-disk interaction theory to substructures in the ALMA DSHARP sample to reveal the potential young planet population. We find that the occurrence rate for >5 M J planets beyond 5-10 au is consistent with direct imaging constraints. Disk substructures allow us to probe a wide-orbit planet population (Neptune to Jupiter mass planets beyond 10 au) that is not accessible to other planet searching techniques. On the other hand, ALMA surveys have suggested that the dust in Class II disks may not be enough to explain the averaged solid mass in exoplanets, under the assumption that the mm disk continuum emission is optically thin. I will question this optically thin scenario and point out that dust scattering can considerably reduce the emission from an optically thick region. This optically thick disk scenario can solve several puzzles in protoplanetary disk observations and can provide enough dust to form exoplanets. Finally, I will talk about my ongoing work on 3-D radiation hydrodynamical simulations of forming Jupiter’s convective envelope. |
| Apr. 13, 2021 | Yamila Miguel Leiden Observatory |
Unveiling the secrets of Jupiter with the Juno mission With more than 4000 exoplanets found and about 2-dozens of planets with detected atmospheric chemical species, we moved from an era of discovery to a new era of exoplanet characterisation. On the other hand, extremely accurate measurements by Juno and Cassini missions, make this an exceptional time to combine the detail information on the solar system giant planets and the large amount of data from exoplanets to get a better understanding on planetary physics and a better comprehension on planet formation and evolution. Because our knowledge on the interior structure of the giant planets is linked with the data we obtain from space missions, these last years were crucial for this field: the outstanding accuracy of the gravity data provided by Juno has fundamentally changed our understanding of the interior of Jupiter. It has allowed us to put constrains on the zonal flows, the extent of differential rotation and lead us to find that Jupiter has most likely a dilute core. In this presentation I will review our knowledge on the interior structure of Jupiter and will also show some new results where we find that a non-homogenous envelope is also a constraint set up by the Juno measurements, which is helping us to get closer to unveiling Jupiter’s deep secrets and to reach a better understanding of the giant planets formation history. |
| Apr. 20, 2021 | Ignas Snellen Leiden Observatory |
Exoplanets and the search for extraterrestrial life Abstract: Placing the solar system in the context of other planetary systems is one of the central objectives driving the study of extrasolar planets. One of the most fascinating questions in modern science is whether other life-bearing planets exist. In this talk I will review the current state of the art of exoplanet research and discuss future ways to probe biomarker gases in Earth-like exoplanets that could point to biological activity. |
| Apr. 27, 2021 | Alberto Bolatto University of Maryland |
The Inner Workings of Starbursts Starbursts are a rare phenomenon in the present day universe, but they represent perhaps the most common mode under which stars form and galaxies grow during the z~1-2 peak of cosmic star formation activity. This mode of star formation is not a simple scaling of what happens in typical molecular clouds, but represents a much more efficient manner of converting gas into stars likely through the formation of massive clusters. The resulting feedback in the form of galaxy-scale outflows is, together with AGN, thought to be one of the main forms of regulation of galaxy growth. I will show the analysis of recent, high resolution observations of three of the nearest starbursts: NGC253, NGC4945, and M82. I will first discuss the properties of their galactic molecular outflows, including our best constraints on the mass and outflow rate, and the properties of the molecular gas. Then I will focus on the results from high-resolution observations which reveal a dozen compact structures with properties corresponding to massive young star clusters and super star clusters (SSCs), most of which are so embedded that are invisible in optical and NIR observations. Finally, I will present the analysis of 0.5-pc resolution observations of NGC253 which reveal feedback and disruption on the scales of these clusters, I will discuss the properties of these "cluster-scale" outflows, and I will compare them to theoretical expectations. |
2020 Fall Colloquium Series
The Fall 2020 Joint Astrophysics Colloquium was held virtually on Tuesdays at 11AM and was followed by the Bahcall Lunch at 12:30, also virtual.
Please find the Fall speaker schedule here. Videos of the talks can be found on the IAS website: https://www.ias.edu/video-tags/iaspu-joint-astrophysics-colloquium
2020 Summer Colloquium Series
The 2020 Summer Colloquium Series led by Professor Jenny Greene has concluded. The list of speakers, talk titles and select colloquium recording links appear below.
| Date | Name | Talk |
|---|---|---|
| Jun 30, 2020 | Evan Schneider | The Origin of Multiphase Galaxy Outflows |
| July 7, 2020 | Courtney Dressing | Exploring Planets Orbiting Nearby Stars |
| July 14, 2020 | Geraldine Cochran | Promoting Diversity and Addressing Barriers in Physics |
| July 21, 2020 | Sean Johnson | Observations of the gas flows that govern galaxy evolution in absorption and emission at z<1 |
| July 28, 2020 | Julie Posselt | Equity in Science: Representation, Culture, and the Dynamics of Change in Graduate Education |
| Aug 4, 2020 | Richard Anantua | A Glimpse into Horizon-Scale Physics Using Movies and Polarization Maps |
| Aug 11, 2020 | Casey Miller | Practicing Equity in Graduate Admission |
| Aug 25, 2020 | Kareem El-Badry | Emission-line stars, binary mass transfer, and the search for detached stellar mass black hole |