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Astrophysics Seminars

Contents

The CASS Astrophysics Seminar features world-class astrophysicists from around the world speaking on current topics of research. Presentations are aimed at the graduate and post-graduate level, but are open to the general public. CASS seminars take place on Wednesdays from 3:00 - 4:00 p.m. in 383 SERF (Marlar Seminar Room), unless otherwise noted. You can watch a live stream of the talk or prior talks at the CASS Seminar YouTube Channel. The organizers are Prof. Quinn Konopacky and Dr. Alexei Kritsuk.


Upcoming Seminars

Winter 2019


February 20, 2019

 "The Wind of Change: create, move, and observe cold gas around galaxies"

Max Gronke
Postdoctoral Scholar
UC Santa Barbara

 Galactic winds are large-scale, multiphase outflows from galaxies and crucial for the galactic ecosystem. They are, thus, a potent probe for the underlying feedback mechanisms. The usual picture is that the cold gas has been accelerated by ram pressure forces due to the hot gas. However, reproducing this ubiquitous observation in hydrodynamical simulations has proven to be challenging - simply because the destruction time is shorter than the acceleration time. During my talk, I will show some analytical estimates and results from recent (magneto-)hydrodynamics simulations which suggest a solution to this classical "entrainment problem". I will conclude by discussing potential implications for larger scale galactic simulations, and observables of cold gas in the surroundings of galaxies. In particular, I want to show that the Lyman-alpha line is a powerful probe of the (small-scale) structure of neutral hydrogen.



February 27, 2019

NOTE: Hans E. Suess Memorial Lecture 4:00-5:00pm in NSB Auditorium
(Reception in NSB Atrium from 3:00-4:00pm)
 "The Search for Life beyond the Solar System"

Victoria Meadows
Professor
University of Washington

 One of the most exciting and interdisciplinary frontiers in exoplanet science is the search for life beyond the solar system. Recently discovered planets, especially Earth-sized planets orbiting nearby red dwarf stars, will provide intriguing near-term targets for large ground-based telescopes and the James Webb Space Telescope, while even larger telescopes are planned to directly image and explore the environments of worlds around stars like our Sun. These telescopes may detect planetary features that suggest a biological origin, but our ability to accurately interpret whether these features are due to life will depend on our understanding of planetary evolution and processes, and environmental context. This talk will provide an overview of the current state of exoplanet biosignature science, and describe interdisciplinary research by NASA’s Virtual Planetary Laboratory team to understand how to identify which planets are most likely to harbor life. I will also describe the VPL’s work to develop a comprehensive framework for exoplanet biosignature assessment by synthesizing research from Earth science, planetary science, stellar astrophysics and biology—and describe the prospects for terrestrial exoplanet characterization and life detection with future telescopes.



March 6, 2019

Joseph Hennawi
Associate Professor
UC Santa Barbara



March 13, 2019

 "The Many Faces of Matter inside of Neutron Stars"

Fridolin Weber
Distinguished Professor of Physics / CASS Research Scientist
San Diego State University / UCSD

 Gravity compresses the matter in the core regions of neutron stars to densities that are several times greater than the density of ordinary atomic nuclei. This provides a high-pressure environment in the core regions of neutron stars where several different subatomic particle processes are expected to compete with each other and even novel states of matter exist. The most spectacular possibilities involve the generation of hyperons and baryon resonances, boson condensates, and/or the formation of color superconducting quark matter. Combined with the unprecedented progress in observational astrophysics, this makes neutron stars superb astrophysical laboratories for a range of physical studies which shed light on the structure and equation of state of dense baryonic matter. In this talk I will begin with providing an overview of our current understanding of the core-composition of neutron stars. Models for the equation of state of dense neutron star matter will then be presented, which are constrained by the latest nuclear and astrophysical data. Particular emphasis will be put on the quark- hadron phase transition in the core regions of neutron stars, which could be driven by changes in the rotation periods of neutron stars. Finally, the phase diagram of hot and dense proto neutron star matter will be discussed and possible instabilities in such matter will be pointed out. The information gained from these investigations provides information about the nuclear equation of state that is complementary to what is expected from the study of gravitational waves from neutron star-black holes and binary neutron star mergers, high baryon density QCD from lattice calculations, and high baryon density physics from low energy heavy-ion collisions at RHIC and GSI.


Spring 2019


March 27, 2019

NOTE: Spring Break - no seminar today



April 3, 2019

Dmitry Savranksy
Assistant Professor of Mechanical and Aerospace Engineering
Cornell University



April 10, 2019

 "A Cosmic Test of Quantum Entanglement and Bell's Inequality: Choosing
Measurements with Light from High Redshift Quasars"

Andrew Friedman
Assistant Research Scientist
UCSD-CASS

 In our recent experimental tests of Bell’s inequality, for the first time, we used observations of astronomical sources to randomly choose measurement settings for polarization-entangled photons sent through free space to two distant detectors. In our 2017 pilot test in Vienna, Austria, we used the color of light from Milky Way stars, and in 2018, we performed the first Cosmic Bell test in the Canary Islands using light from high redshift quasars. In both sets of tests, we observed statistically significant violation of Bell’s inequality, implying that John Bell’s very reasonable assumptions about the world cannot all be true in nature. These assumptions include realism/determinism, locality, and experimental freedom of choice. Our tests aim to put tension on the latter assumption, arguably the most subtle of Bell’s axioms, which holds that each detector’s measurement choices are completely free of any non-quantum degrees of freedom in the causal past of the experiment that could also affect the measurement outcomes. Since the nearest star in the pilot test was ~600 light years away, given our assumptions, the observed Bell violation implies that any non-quantum explanations for entanglement must have been in place prior to ~600 years ago, an improvement of ~16 orders of magnitude compared to previous tests. Similarly, since the nearest quasar in our best experimental run was 7.8 billion light years away, any such mechanism is relegated an additional ~6 orders of magnitude into the cosmically distant past, corresponding to excluding non-quantum explanations from 96% of the space-time volume in the causal past of the experiment. In addition to exploring how free our experimental choices are while investigating the fundamental nature of reality in the subatomic world, such foundational tests are relevant to whether practical quantum encryption schemes will ultimately be as secure as many researchers believe. Our other new theoretical work shows that relaxing freedom of choice by a relatively small amount can still reproduce the quantum predictions, making the associated loophole easier to exploit than other well known entanglement test loopholes.



April 17, 2019

Yong Zheng
Miller Postdoctoral Fellow
UC Berkeley



April 24, 2019

Tina Kahniashvili
Associate Research Professor
Carnegie Mellon University



May 15, 2019

Richard Lingenfelter
Research Physicist Emeritus
UCSD-CASS



May 29, 2019

Arun Surya
Postdoctoral Scholar
UCSD-CASS



June 5, 2019

Greg Mace
Research Associate
University of Texas, Austin



June 12, 2019

Melville Ulmer
Professor
Northwestern University