TAP @ UA
  • Home
    • Calendar
    • News
  • About
  • Colloquia
    • Media
    • Posters
  • Initiatives
    • Computation and Data
    • Cosmology
    • Gravity
    • Planet Formation
    • Plasma Physics
  • Visitor Series
  • Members
  • Student Programs
  • The University of Arizona
Select Page

TAP Colloquia on YouTube

TAP - University of Arizona

TAP - University of Arizona
YouTube Video VVVnalEtOEJOZVZrWklHUDlnMndTQkRRLlhJNjRrMXBsT3dJ TITLE Towards Ultra High-Resolution Simulations of Giant Impacts ABSTRACT Giant impacts (GI) represent a crucial stage in the formation and evolution of planetary systems, determining their final structure, constituent masses, and compositions, as well as the presence of satellites. Because these global scale collisions cannot be investigated in laboratory experiments, numerical simulations are an important tool to study their outcomes. With several examples of giant impact simulations, I highlight the interplay between equation of state and numerical resolution and motivate the need for new codes. In the second part of the talk, I present our new smoothed particle hydrodynamics (SPH) code pkdgrav3 and demonstrate its capabilities.
TITLE Towards Ultra High-Resolution Simulations of Giant Impacts ABSTRACT Giant impacts (GI) represent a crucial stage in the formation and evolution of planetary systems, determining their final structure, constituent masses, and compositions, as well as the presence of satellites. Because these global scale collisions cannot be investigated in laboratory experiments, numerical simulations are an important tool to study their outcomes. With several examples of giant impact simulations, I highlight the interplay between equation of state and numerical resolution and motivate the need for new codes. In the second part of the talk, I present our new smoothed particle hydrodynamics (SPH) code pkdgrav3 and demonstrate its capabilities.
TITLE Why is machine learning for fundamental science different? ABSTRACT Machine learning and artificial intelligence are very trendy topics in virtually every part of modern society now. However, the tremendous success seen in the broader society does not seem to transfer to fundamental science as much as we hope it to be. What are the reasons behind such differences? And how should we think of using machine learning in fundamental science research? In this talk, I will illustrate some of my opinions on this through some successes and failures the gravitational wave community had in applying machine learning methods. BIO Kaze W. K. Wong is a Flatiron research fellow at the Center for Computation Astrophysics, Flatiron Institute. His research primarily focuses on developing machine learning-enhanced algorithms and software for astrophysics. He earned his Ph.D. from Johns Hopkins University in physics and astronomy in 2021 and his bachelor degree from The Chinese University of Hong Kong in 2017. He was awarded the GWIC Thesis Prize for his distinct contribution to building Machine-learning-enhanced tools for gravitational-wave data analysis.
TITLE: New Perspectives on Diagnosing Electron Energization in Magnetic Reconnection ABSTRACT: Magnetic reconnection is a ubiquitous process in space and astrophysical plasmas, and it plays a fundamental role in transforming stored magnetic energy into particle kinetic and thermal energies. Reconnection is thought to produce high energy, non-thermal particles in a variety of systems, including gamma ray bursts, solar and stellar flares, and pulsar magnetospheres. In addition to non-thermal electron production, reconnection also leads to significant thermal energization of both ions and electrons. The thermal heating due to reconnection plays an important role in many systems, including heating the solar corona and accelerating the solar wind, providing electron heating in Earth’s geospace environment, and dissipating energy in the myriad turbulent systems that pervade the universe. Particle energization in magnetic reconnection has traditionally been examined from a particle, or Lagrangian, perspective using particle-in-cell (PIC) simulations. Guiding-center analyses of PIC particles has suggested that Fermi (curvature drift) acceleration and direct acceleration via the reconnection electric field are the primary electron energization mechanisms. However, both PIC guiding-center analyses and spacecraft observations are performed in an Eulerian frame. We employ the continuum Vlasov-Maxwell solver within the Gkeyll simulation framework to re-examine electron energization in reconnection from a continuum, Eulerian perspective. We separately examine the contribution of each drift energization component to determine the dominant electron energization mechanisms in a moderate guide-field Gkeyll reconnection simulation. We compare the Eulerian (Vlasov Gkeyll) results with the wisdom gained from Lagrangian (PIC) analyses. Time permitting, we will also present the phase-space signature of direct electron acceleration in the large guide magnetic field limit using the field-particle correlation technique. BIO: Jason TenBarge is a Research Scholar at Princeton University in the Department of Astrophysical Sciences and at the Princeton Plasma Physics Laboratory. Dr. TenBarge studies basic plasma processes by applying and developing analytical and numerical tools to understand kinetic dissipation and transport processes in space and astrophysical plasmas. He received degrees in Astrophysics and Mathematics from Indiana University in 2003 and a physics Ph.D. in 2009 from the University of Texas at Austin, where his research focused on relativistic plasma astrophysics. From 2009 to 2013, he worked as a postdoctoral research associate at the University of Iowa studying solar wind turbulence. Afterward, he moved to the University of Maryland College Park as a research scientist from 2013 to 2017. In 2017, he joined the astronomy and plasma physics group at Princeton University.
TITLE: Illuminating the Dark Universe with Low-mass Galaxies ABSTRACT: Dark matter is a mysterious component in the current standard model of cosmology. Because dark matter is not directly observable, the interpretation of the results from dark matter experiments and astronomical surveys often relies on, and sometimes is limited by, our understanding of the relation between visible galaxies and the dark cosmic structures (dark matter halos). In this talk, I will discuss the recent progress in modeling important features of this so-called galaxy-halo connection, in particular in the low-mass regime that is increasingly relevant to the upcoming deep observations, such as the Rubin Observatory LSST. I will discuss a few theoretical advances, including how the halo-subhalo interaction impacts the galaxy-halo connection, and the degree at which the galaxy assembly depends on halo assembly (also known as assembly bias). I will also discuss some recent observations of low-mass galaxies in the nearby universe that have propelled these theoretical advances, and how we are prepared to explore the nature dark matter with upcoming observations. BIO: Dr. Yao-Yuan Mao is an Assistant Professor of Physics and Astronomy at the University of Utah, studying astrophysics with a focus on low-mass galaxies and dark matter. His research answers key questions about the nature of dark matter, galaxy formation physics, and the uniqueness of our own Milky Way by studying the connection between visible galaxies and their invisible nests, the dark matter halos. Yao received a Ph.D. in Physics from Stanford University in 2016, conducted postdoctoral research at the University of Pittsburgh as a Samuel P. Langley PITT PACC Fellow (2016–19) and later at Rutgers University as a NASA Einstein Fellow (2019–22).
TITLE: Magnetism and morphology in the interstellar medium ABSTRACT: The interstellar medium (ISM) is a turbulent, multi-phase, magnetic environment. Magnetic fields thread our Milky Way Galaxy, influencing interstellar physics from cosmic ray propagation to star formation. The magnetic interstellar medium is also a formidable foreground for experimental cosmology, particularly for the quest to find signatures of inflation in the polarized cosmic microwave background. Despite its importance across scientific realms, the interstellar magnetic field and its influence on Galactic processes are not well understood. Dr. Clark will discuss new ways to probe interstellar magnetism and the phase structure of interstellar gas, with a particular focus on morphology: how the spatial structure of gas and dust encodes information about the physics of the ISM. BIO: Susan Clark is an Assistant Professor of Physics at Stanford and a senior member of Stanford's Kavli Institute for Particle Astrophysics and Cosmology (KIPAC). Clark is an astrophysicist with primary research interests in cosmic magnetic fields, magnetohydrodynamic processes, and the interstellar medium. She leads the Cosmic Magnetism & Interstellar Physics group at Stanford, working to solve open questions in the field with a combination of observation, simulation, and analytic theory. Prior to joining the faculty at Stanford, Clark was a NASA Hubble Fellow and postdoctoral member at the Institute for Advanced Study in Princeton, New Jersey. She earned her Ph.D. in 2017 from Columbia University, where she was an NSF Graduate Fellow. She did her undergraduate work at the University of North Carolina at Chapel Hill on a Morehead-Cain scholarship.
ABSTRACT: We stand at an incredible time in exoplanet science, about to characterize worlds outside the solar system in great detail. The exquisite capabilities of JWST will allow us to see the atmospheres of planets from super-Jupiters to sub-Neptunes to Earths. Dr. Morley will discuss two aspects of exoplanet atmosphere science as it stands in early 2023, on the cusp of this revolution. First, she will discuss our path to observing true Jupiter analogs, which takes us through observations of the coldest brown dwarfs and directly-imaged planets. Next, she’ll discuss how atmosphere loss may be sculpting the atmospheres of planets, both large and small, with huge implications for the next five years of studying Earth-sized planets with JWST. BIO: Caroline Morley is an Assistant Professor at the University of Texas at Austin, studying the atmospheres of planets large and small. She got her B.S. from MIT in 2010 and her Ph.D. from the University of California at Santa Cruz in 2016. She specializes in modeling the atmospheres of planets and brown dwarfs, including the effects of clouds and hazes on their spectra.
TITLE: Galaxies Lacking Dark Matter ABSTRACT: The standard cold dark matter plus cosmological constant model predicts that galaxies form within dark-matter halos and that low-mass galaxies are more dark-matter dominated than massive ones. The unexpected discovery of two low-mass galaxies lacking dark matter immediately provoked concerns about the standard cosmology and ignited explorations of alternatives, including self-interacting dark matter and modified gravity. Apprehension grew after several cosmological simulations using the conventional model failed to form adequate numerical analogs with comparable internal characteristics (stellar masses, sizes, velocity dispersions, and morphologies). Here we show that the standard paradigm naturally produces galaxies lacking dark matter with internal characteristics in agreement with observations. Using a state-of-the-art cosmological simulation and a meticulous galaxy-identification technique, we find that extremely close encounters with massive neighbors can be responsible for this. We predict that ~30% of massive central galaxies (with at least 1e11 solar masses in stars) harbor at least one dark-matter-deficient satellite (with 1e8–1e9 solar masses in stars). This distinctive class of galaxies provides an additional layer in our understanding of the role of interactions in shaping galactic properties. Future observations surveying galaxies in the aforementioned regime will provide a crucial test of this scenario. BIO: Jorge Moreno is a theoretical astrophysicist with expertise in galaxy evolution and an Assistant Professor of Physics and Astronomy at Pomona College (promotion to Associate Professor effective July 1st, 2023). Prof. Moreno employs high-performance supercomputers to simulate galaxy assembly, has published ~50 peer-reviewed articles, and has delivered over 100 invited colloquia worldwide. In addition to being a world-renowned scientist, Prof. Moreno is an award-winning teacher and mentor who is devoted to decolonizing their classroom, mentoring style, and research philosophy -- including the creation of anti-hierarchical classrooms, decolonizing symposia, the interrogation of violent language in their discipline and the proposition of astromimicry as a blueprint to create more welcoming academic spaces.
ABSTRACT: Fast inward migration of planetary cores embedded in gaseous disks is a common problem in the current planet formation paradigm. Even though dust is ubiquitous in protoplanetary disks, its dynamical role in the migration history of planetary embryos has not been considered until recently. In this talk, Dr. Pessah will show that the scattered dust/pebble-flow induced by a low-mass planetary embryo leads to an asymmetric dust/pebble-density distribution that is able to exert a net torque. Building on the results of a large suite of numerical simulations for measuring this dust torque under a wide range of conditions, Martin will present the first study quantifying the role of dust in the migration history of low-mass planets. BIO: Dr. Pessah started his career at the University of La Plata in Argentina and obtained his Ph.D. as a Member of the Theoretical Astrophysics Program at the University of Arizona in 2007. He was a member of the Astrophysics Group at the Institute for Advanced Study in Princeton from 2007 to 2010. Later he became Assistant Professor at the Niels Bohr Institute in Copenhagen, where he founded the Theoretical Astrophysics Group in 2010. Currently, Martin is a Professor in Theoretical Astrophysics at the Niels Bohr International Academy, where he also acts as Deputy Director. Martin has broad research interests in astrophysical dynamics spanning protoplanetary disks, black hole accretion disks, galaxy clusters, black hole binaries, and tidal disruption events.
ABSTRACT: The origin of the heaviest elements in our universe - those produced via the rapid neutron capture process ("r-process") - remains a question of intense debate. Although the kilonova emission that accompanied GW170817 revealed neutron star mergers to be an important r-process source, several independent observations hint that mergers may not be the only source, particularly at low metallicity. I will argue that mass-loaded outflows from the accretion disk feeding the newly-formed black hole - that responsible for powering the gamma-ray burst (GRB) jet - was the dominant source of r-process elements in GW170817. However, broadly similar accretion flows are created in another explosive transient - the collapse of massive rotating stars ("collapsars") which give rise to GRBs of longer duration, and simple estimates show that the integrated r-process yields of collapsars could compete with those of neutron star mergers over the history of the Galaxy. I will discuss observational tests of whether collapsars produce r-process elements using infrared observations of GRB supernovae, particularly with JWST and the Roman Space Telescope. BIO: Brian Metzger received his Bachelor's degrees at the University of Iowa and his Ph.D. at UC Berkeley in 2009. He held a NASA Einstein Postdoctoral Fellowship at Princeton, before joining the Columbia Department of Physics in 2013, where he is currently a full professor. He is also a Senior Research Scientist in the Center for Computational Astrophysics at the Flatiron Institute. His recognitions include the Sloan Fellowship; the New Horizons Breakthrough Prize in Physics; the Bruno Rossi Prize of the American Astronomical Society; and the 2020 Laureate of the Blavatnik Awards for Young Scientists. He is supported as a Simons Investigator by the Simons Foundation.
Load More... Subscribe
QUESTIONS? SITE MANAGEMENT (c) 2022 Theoretical Astrophysics Program, University of Arizona