List of Past Astronomy Colloquia : 01-Jan-2022 to 01-Jun-2022

Date:   Wednesday 02-Feb-2022
Speaker:   Ray Pierrehumbert (Halley Prof. at Oxford)
Title:  Climate of temperate subNeptunes

subNeptunes are low-density planets that are generally somewhat larger in radius than Earth but still considerably smaller than Uranus or Neptune. Their low densities mean that they cannot be composed primarily of rock an Iron (like Earth or Venus) but must instead have a very extensive low molecular weight volatile envelope. There are nonetheless many possible compositions and structures that can fit into the characteristics of a subNeptune. subNeptunes are very common in the catalogue of known exoplanets, and they may well be the most common kind of planet in the Universe. Temperate subNeptunes are subNeptunes that have an installation that, for a rocky planet, would put them in the nominal habitable zone, and they have attracted attention in part because of the hypothetical possibility of life in water clouds; water vapour condensation also makes them interesting from a basic dynamical standpoint. In this talk, I will discuss the radial structure of subNeptunes, the meaning of the concept of “runaway greenhouse” as applied to subNeptunes, and the general circulation of temperate subNeptune atmospheres.

Date:   Wednesday 09-Feb-2022
Speaker:   Dr. Ekta Patel (UC Berkeley)
Title:  Dynamics of Local Group Satellite Galaxies in the Era of Precision Astrometry

High-precision astrometric data from space observatories, such as the Hubble Space Telescope (HST) and Gaia, are revolutionizing our ability to study the Local Group. 6D phase space measurements (3-dimensional position and velocity) now make it possible to rewind the clock and trace the orbital histories of nearly half of all Local Group satellites to their cosmic origins in the early Universe. These new datasets pave the way for a revised model of the Local Groups dynamical history and its current dark matter content. In this talk, I will focus on the Magellanic Clouds and M33, the most massive satellite galaxies orbiting around the MW and M31, respectively. These massive satellites are nearly 10% as massive as their host galaxies and LCDM simulations predict that they too host a population of "ultra-faint satellite galaxies, i.e. a satellites of satellites hierarchy. I will juxtapose these two satellite systems and discuss ongoing efforts to characterize satellites of the Magellanic Clouds and future efforts for finding M33 satellites. Together, these two systems provide a direct test for LCDM predictions at the low mass end and act as a benchmark for next generation studies of analogous galaxies beyond the Local Group in the era of Roman, JWST, and LSST.

Date:   Wednesday 16-Feb-2022
Speaker:   Dr. Chris Reynolds (Cambridge)
Title:  Probing the extremes with clusters of galaxies

Clusters of galaxies provide a wonderful laboratory for studying extreme physics and astrophysics. In this talk, I will conduct a whirlwind tour of some of these investigations, both theoretical and observational. Firstly, I will show that the cores of relaxed galaxy clusters are one of the best environments to study facets of active galactic nucleus (AGN) feedback. Examining the physics at play in these feedback processes necessitates a hard look at the plasma physics of the hot intracluster medium that permeates the cluster, leading us to new understandings of processes as basic as thermal conduction. Secondly, the galaxies at the centers of relaxed clusters, and the supermassive black holes that they host, are amongst the most massive in the Universe. I will discuss these unusual central cluster AGN and present X-ray based spin measurements of the black hole in one remarkable cluster, CL1821+643, which sheds light on the growth mode of the most massive supermassive black holes. Thirdly, I will discuss the use of galaxy clusters for fundamental physics and, in particular, the extraordinary constraints that they set on certain extensions of the standard model of particle physics (namely axion-like particles). I will end with a brief discussion of the future prospects of these studies in the light of the recent Decadal survey recommendations.

Date:   Wednesday 23-Feb-2022
Speaker:   Dr. Eileen Gonzales (Cornell University)
Title:  Peering Through the Clouds: Investigating Substellar Atmospheres

Brown dwarfs and directly imaged self-luminous exoplanets are interesting and complex worlds that form a critical stepping stone along the path to imaging Earth-like planets. By examining their atmospheres in detail we can better understand their thermal profiles, chemical composition, and cloud properties that are tightly coupled with their formation and evolution. In this talk, I will explain how I use atmospheric retrievals, a powerful inverse modeling technique, to examine the atmospheres of brown dwarfs. I will present results from a comparative sample of brown dwarfs showing how they have enhanced our understanding of the atmospheres of substellar objects and our retrieval approach. Lastly, I will discuss how JWST and next-generation observatories will enhance our understanding of substellar atmospheres serving as a critical bridge in our exploration of smaller and cooler worlds.

Date:   Wednesday 02-Mar-2022
Speaker:   Dr. Josh Simon (Carnegie Observatories)
Title:  Dwarf Galaxies as Astrophysical Laboratories

The dwarf galaxies orbiting the Milky Way are the oldest, least luminous, most dark matter-dominated, and least chemically evolved stellar systems known. To begin, I will provide a brief introduction to these galaxies, highlighting the recent discovery of large numbers of ultra-faint dwarf galaxies. I will then explain how we can measure their dark matter content and describe some of the numerous ways that dwarfs are being used to constrain the properties of dark matter. Finally, I will show how chemical abundance measurements of dwarf galaxy stars provided critical insight into r-process nucleosynthesis prior to the LIGO discovery of a neutron star merger.

Date:   Wednesday 09-Mar-2022
Speaker:   Dr. Tom Jarrett (Univresity of Cape Town)
Title:  Immersive Data Exploration: Formulating the Definitive Local Universe Benchmark

In this presentation I will highlight two topics of active research in my sphere: scientific visualization of spectral imaging and large-scale structure using VR technology, and benchmarking the local star formation main sequence using exquisite WISE imaging and measurements of the local universe. To start with, we have developed a software system that enables user-interaction and immersive exploration of 3D data, notably designed to work with HI spectral cubes from radio interferometers. I present the beta release of iDaVIE-v (immersive Data Visualization Interactive Explorer for volumetric rendering), which combines virtual reality (VR) technology and custom-built software to work with particle and volume data sets. Originally developed to serve the HI Radio Astronomy community for HI source identification, the software is now in the public sphere, with capabilities that will serve the broader astronomy community (e.g., redshift catalogues, cosmological simulations). I show examples in which the VR software has been used to analyze real data from the SKA Pathfinders, and notably report on the MeerKAT discovery of an extraordinary HI cloud complex found using this technology. And finally, I will give a sneak peak at the galaxy-evolution results coming from the WISE infrared study of over 10K galaxies carefully measured and characterized since the launch of WISE over 10 years ago.

Date:   Wednesday 16-Mar-2022
Speaker:   Dr. Adam Ginsburg (University of Florida)
Title:  Star Formation and Mass Measurements in the Galaxy

The most important factor deciding the fate of a star and its surroundings is its initial mass. The relative number of high- and low-mass stars decides how much light and mass escape from a population of stars. This distribution, the stellar initial mass function, is often assumed to be universally invariant, though we have plenty of reason to believe it varies with environment. I will present results from and previews of several ALMA programs that measure the mass distribution of pre- and proto-stellar objects at early phases. Core mass function measurements suggest that more intensely star-forming regions preferentially form high-mass stars. On larger scales, the degree of clustering varies with environment: more stars form in clusters in the Galaxy's Central Molecular Zone than in the Galactic disk. Measuring these environmental effects in the Galaxy, where we can resolve the individual stars but still recover the larger environment, gives us a firm footing on which to base star formation theories. However, measurements of pre- and proto-stellar mass remain challenging, so throughout this talk, I will emphasize techniques we are developing and using to improve mass measurements at early stages of star formation, including kinematic measurements using brinary disks.

Date:   Wednesday 23-Mar-2022

Date:   Wednesday 30-Mar-2022
Speaker:   Dr. Ulrich Steinwandel (Flatiron Institute)
Title:  Advances in galaxy formation through numerical simulations

Recent numerical simulations of galaxy formation have begun to model the details of the interstellar medium (ISM) in evermore detail. This includes accurate treatments for hydrodynamical flows with accurate mixing behavior, non-equlibrium cooling and chemistry, as well as the feedback of massive stars in terms of their UV-radiation, photoelectric heating rate and supernova-feedback. The most recent iterations of these models are capable to self-consistently follow the build-up of the hot phase and the momentum of the ISM by resolving the Sedov-Taylor phase of individual supernova events. In my talk I will present results from the GRIFFIN stellar feedback model that is designed for treating the ISM at solar mass and sub-parsec resolution in global simulations of galactic discs to properly study the build-up of resolved galaxy outflows. These state-of-the-art simulations of galactic outflows allow for the first time for an accurate comparison with observed outflows and can heavily contribute to a better theoretical understanding of outflows by providing us with detailed wind loading factors across different mass scales based on a model that can resolve the details of wind launching self-consistently.

Date:   Wednesday 06-Apr-2022
Speaker:   Dr. Joyce Yen (University of Washington)
Title:  Effective Evaluation Practices: Evidence from research on bias and its consequences

While many individuals and organizations in science and engineering state they support diversity, equity, and inclusion, every day practices may prevent such statements from becoming a reality. In this talk we examine one area were individuals and organizations can actively become more inclusive and effectively advance diversity goals: application evaluation. After defining diversity to provide a framework for this talk, we will review evidence from research on bias and its consequences, examine effective evaluation practices, and demonstrate how diversity, equity and inclusion is a leadership issue that requires actions, rather than statements, of commitment.

Date:   Wednesday 13-Apr-2022
Speaker:   Dr. Igor Andreoni (UMD)
Title:  Seize the night in the era of wide-field optical surveys

We are living in a golden era for optical time-domain astronomy. Wide-field surveys such as the Zwicky Transient Facility (ZTF) image most of the observable sky every night, opening a discovery space historically difficult to explore in the optical. The ability to crunch big data efficiently has become key to discovery. In this colloquium, I will present results for two science cases in particular that we have directly addressed with ZTF real-time searches. These include binary neutron star mergers and special tidal disruption events, which are great multi-messenger sources. I will present results from both "triggered" and "serendipitous" transient searches with ZTF as well as prospects for the upcoming Vera C. Rubin Observatory, which is expected to produce millions of transient alerts every night.

Date:   Wednesday 20-Apr-2022
Speaker:   Dr. Alan Stern (SWRI)
Title:   In Honor of Professor Mike A'Hearn: The Exploration of Pluto and the Kuiper Belt

Date:   Wednesday 27-Apr-2022
Speaker:   Dr. Jenny Bergner (University of Chicago)
Title:  Volatile chemistry in planet-forming disks

Planets form within disks composed of gas, ice, and dust in orbit around young stars. The distribution of volatiles (gas+ice) within these disks profoundly impacts both the chemical and physical outcomes of planet formation-- including the delivery of prebiotic building blocks to new worlds. In this talk, I will highlight our recent advances in disentangling how organic complexity is built up during the star and planet formation sequence, the role of interstellar inheritance in setting disk volatile compositions, and the distinctive volatile chemistry at play during the planet formation epoch. These insights are gained by combining telescope observations, ice chemistry experiments, and disk simulations, each of which contributes an indispensable piece of the puzzle. Taken together, we are assembling a more complete picture of the chemical environment which regulates the formation, composition, and potential habitability of planetesimals and planets.

Date:   Wednesday 04-May-2022
Speaker:   Dr. Dan Coe & Brian Welch (STScI & JHU)
Title:  Observing the First Galaxies and a Distant Star with Hubble, JWST, and Gravitational Lensing

Hubble has revealed galaxies 97% of the way back to the Big Bang. The most distant appear to us as pale infrared dots. Gravitational lensing magnifies some early galaxies, enabling us to study them in detail down to parsec-scale star clusters and even an individual star, Earendel recently discovered at z = 6. JWST will study Earendel and the first galaxies, showing us what they are made of: perhaps including pristine Population III stars, or perhaps already enriched with heavy metals. JWST will observe lensed galaxies as distant as MACS0647-JD at z = 11 and finally reveal even more distant galaxies in the first 3% of cosmic history, the first 400 million years. I predict lensing will be the key to discovering the first galaxies with JWST.

Date:   Wednesday 11-May-2022
Speaker:   Dr. Fred Lamb (University of Illinois)
Title:  U.S. Ballistic Missile Defense: Threats and Challenges"

During the past 70 years, the United States has invested more than $350 billion in ballistic missile defense, mostly on systems intended to intercept long-range, nuclear-armed missiles that might be launched against the United States by countries such as North Korea. But would these systems be reliable and effective against such an attack? This question was addressed by a new technical report commissioned by the American Physical Societys Panel on Public Affairs. As I will describe, the report noted that despite decades of effort, no missile defense system thus far developed has been shown to be effective against realistic ICBM threats (ICBMs are ballistic missiles with a range of more than 3,500 nautical miles). The report found that the capabilities of U.S. systems intended to defend against the nuclear-armed ICBMs North Korea may have or could obtain are currently low and will likely continue to be low for the next 15 years.

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