Astronomy Colloquium

Thursday, March 5th, 2020
TBD
Host: 
Timbie
Speaker: Dr. Eric Switzer NASA/Goddard

 

Available Downloads:

Room and Building: 
4421 Chamberlin Hall
Diffusion and transport processes in turbulent plasmas constitute fundamental astrophysical problems; a clear understanding of these processes is needed in order to produce improved theoretical models for the diffusion and transport of energetic particles, including cosmic rays.
Magnetohydrodynamic (MHD) turbulence structured by a large-scale magnetic field is an essential aspect of interstellar or interplanetary plasmas. Here we investigate how turbulent diffusion and dispersion differ in the directions parallel and perpendicular to the magnetic field. We adopt the Lagrangian viewpoint, the natural point of view to study diffusion, and construct statistics based on the trajectories of Lagrangian tracer particles. From the motions of these tracer particles, we evaluate Lagrangian statistics for single-particle diffusion, two-particle dispersion, and velocity autocorrelations. We also demonstrate new Lagrangian statistics developed to understand anisotropic turbulent dispersion. Results will be presented from simulations with grid sizes up to 2048^3.

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Host: 
Professor Ellen Zweibel
Speaker: Professor Jane Pratt Georgia State University, Physics and Astronomy Deparment

 

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Room and Building: 
4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
The interstellar medium (ISM) is the fuel of star formation, and its scattering and absorption of light transforms the Galactic radiation field. Despite its importance, most observations of the Milky Way's ISM are limited to two dimensions; its angular distribution is precisely measured, but its distribution in distance is much more uncertain. Large surveys of stars can be used to resolve this uncertainty. Because light from stars is absorbed and scattered by intervening material before observation on earth, the Galaxy's stars can be used as a dense network of lighthouses, effectively x-raying the ISM to reveal its 3D structure and properties. In this talk, I'll describe our ongoing program to use large surveys to map the ISM in 3D. We have mapped the density of dust in the ISM over the nearest 5 kpc at unprecedented resolution, highlighting complex networks of diffuse voids and dense star-forming regions. We have also been able to measure the size distribution of dust grains throughout the Milky Way, revealing kiloparsec-scale structures that may track variations in the Galactic star-formation rate and gas density. Numerous other projects are possible, ranging from studies of the 3D kinematics of the ISM to the Galactic magnetic field. New surveys and instruments like Gaia, SDSS-V, LSST, and JWST promise a bright future for 3D studies of the ISM, offering incredibly accurate distance measurements, order-of-magnitude larger samples of stars, and unrivalled sensitivitity.
Host: 
Bob Benjamin, UWM
Speaker: Dr. Eddie Schalfly Lawrence Berkeley National Laboratory

 

Available Downloads:

Room and Building: 
4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
The Gaia satellite is currently mapping the phase-space of a few million stars in the solar neighborhood showing time-varying phenomena. About 350,000 stars within 200 pc of the Sun are identified in streams, bundles of stars that move together in the same direction with a velocity that is distinct from neighboring stars. I will present a set of N-body simulations of the Milky Way disk that shows the role of a long stellar bar and spiral arms in understanding the complex kinematics of the solar vicinity. Finally, the passage of Sagittarius dwarf galaxy induces rapid time-variations in the potential that lead to a significant bias of the Oort limit through the Jeans modeling. This calls for the development of non-equilibrium methods to estimate the dynamical matter density locally and in the outer disk.
Speaker: Professor Elena D'onghia UW Madison Astronomy Department

 

Available Downloads:

Room and Building: 
4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
High-mass stars are responsible for some of the most spectacular astronomical objects such as supernova remnants and stellar mass black holes. High-mass stars form in giant molecular clouds, generate copious amounts of ionizing photons responsible for the development of HII regions, and drive ionized jets and massive molecular outflows that contribute to the dissipation of their natal clouds. Highlights of a multi-scale effort by our group to investigate jets and outflows in high-mass star forming regions will be presented. A central component of our work has been student involvement in the search and characterization of atomic and molecular tracers of jets, outflows and the expansion of ionized gas at microwave frequencies. In particular, we are studying molecular masers as tracers of dynamic phenomena in high-mass star forming regions, including long-term variability and periodic flares, which could be indicative of episodic accretion events in young binary systems.
Host: 
Ed Churwell, Emeritus professor
Speaker: Esteban Araya Western Illinois

 

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Room and Building: 
4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
Feedback from young, super star clusters (SSCs) is a major driver for galaxy evolution at all cosmic epochs, but may be especially relevant for cosmic reionization. The standard scenario for massive-star feedback has been that superwinds from SSCs clear pathways for Lyman continuum (LyC) and Ly-alpha radiation to escape from host galaxies. However, theoretical predictions indicate that for the most massive and compact SSCs, superwinds are actually suppressed by catastrophic cooling and pressure confinement. These extreme conditions are rare, but observational evidence from local starbursts increasingly supports this scenario. I will present our work in establishing this new paradigm and its consequences for LyC and Ly-alpha escape.
Host: 
Professor Amy Barger
Speaker: Sally Oey University of Michigan

 

Available Downloads:

Room and Building: 
4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
The stellar mass of star forming galaxies is thought to increase in a quasi-steady state, where the rate depends on the gas fraction and star formation efficiency, which evolve with redshift. Galaxy mergers can lead to more rapid growth while active galactic nuclei have been argued to play an important role in halting star formation. These processes are tied together through the multi-phase interstellar medium. I will discuss programs exploring so-called "dense gas" tracers and the behavior of starbursts in merging dwarf galaxies. I will also describe a theoretical/modeling program to use galaxy formation simulations as "ground truth" for interpreting observational tracers of the ISM. This use of multiwavelength tracers and hydrodynamic simulations probes galaxy evolution along axes of nuclear activity, redshift, gas fraction, and metallicity. From these studies I will show new results on identification of heavily obscured AGN and intriguing differences in how mergers affect the evolution of high gas fraction galaxies.
Host: 
Professor Emeritus Jay Gallagher
Speaker: George Privon University of Florida

 

Available Downloads:

Room and Building: 
4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
According to modern cosmology, invisible dark matter and dark energy drive the evolution of the universe – and astrophysicists are still working out the implications. Newton’s laws explained why planetary orbits are elliptical, but not why the planetary orbits in the solar system are nearly circular, in the same plane, and in the same direction as the sun rotates. Laplace explained this as a consequence of angular momentum conservation as the sun and planets formed in a cooling and contracting protoplanetary gas cloud. For similar reasons, many astronomers once thought that galaxies would start as disks. But Hubble Space Telescope images of forming galaxies instead show that most of them are prolate – that is, pickle-shaped. This turns out to be a consequence of most galaxies forming in prolate dark matter halos oriented along massive dark matter filaments. This colloquium will include background on the 2019 Nobel Prize in Physics to Jim Peebles “for theoretical discoveries in physical cosmology” [1] and the 2020 Lilienfeld Prize of the American Physical Society to Joel Primack “for seminal contributions to our understanding of the formation of structure in the universe, and for communicating to the public the extraordinary progress in our understanding of cosmology” [2].
[1] https://www.nobelprize.org/prizes/physics/2019/prize-announcement/,
nobelprize.org/uploads/2019/10/advanced-physicsprize2019.pdf.
[2] https://www.eurekalert.org/pub_releases/2019-08/aps-aa2082719.php,
https://news.ucsc.edu/2019/09/primack-lilienfeld-prize.html. (See also Primack’s popular article
https://www.americanscientist.org/article/why-do-galaxies-start-out-as-c....)
Host: 
Professor Tremonti and Professor Bershady
Speaker: Joel Primack UC Santa Cruz

 

Available Downloads:

Room and Building: 
4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
A layer of complexity is missing from the prevailing standard stellar evolution model. Peculiar stars, particularly those found in coeval, isometallic systems like open clusters, play a critical role in its refinement. The blending of stellar light in densely populated clusters poses a formidable challenge in the generation of high-precision light curves. To mitigate such concerns, our team produced an image subtraction pipeline that reveals a diverse population of periodic variables in the K2 dataset. This technique has unveiled new candidate exoplanets, eclipsing binaries, rapidly rotating stars, and pulsating variables. Moreover, we detect sources that are not revealed by other methods, indicating that the image subtraction technique is required to fully exploit cluster fields. I discuss the potential of utilizing cluster variables to probe critical open questions in stellar astrophysics.
Host: 
Professor Robert Mathieu
Speaker: Melinda Soares Princeton University

 

Available Downloads:

Room and Building: 
4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
Novae are the result of thermonuclear flashes on the surfaces of hydrogen-accreting white dwarfs. With peak luminosities in the hundreds of thousands of solar luminosities and roughly fifty detected in M31 each year, novae comprise a well-observed class of stellar transients from radio to X-ray. I will review the current understanding of nova evolution and highlight successes we have had in modeling the post-outburst phase of evolution to connect observable quantities to white dwarf parameters. I will close by introducing the lingering puzzle of observed oscillations in the post-outburst phase and our attempts to explain it.
Host: 
Professor Richard Townsend
Speaker: Bill Wolf UW Eau Claire

 

Available Downloads:

Room and Building: 
4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM

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