Joint IAS Princeton University Astrophysics Colloquium 

2021 Spring Colloquium Series

The Spring 2021 Joint Astrophysics Colloquium will be held virtually on Tuesdays at 11AM and will be and will be followed by the Bahcall Lunch at 12:30, also virtual.

Date   Name    Talk video link (pvt)
Feb. 2, 2021 Eliot Quataert
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
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 will be held virtually on Tuesdays at 11AM and will be followed by the Bahcall Lunch at 12:30, also virtual.  Please find the Fall speaker schedule here.

Videos on IAS website:

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