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Northwestern University

Weekly Astrophysics Seminars 2017-2018

Seminars are held at 4:00 PM on Tuesdays in Room F160
on the first floor of the Technological Institute (2145 Sheridan Road) unless otherwise noted


Winter Quarter 2018

  Date      Speaker / Seminar Host
  Jan. 16

Todd Thompson
   Ohio State University
    Physics and Phenomenology of Galactic Winds

Galactic winds are a crucial ingredient in galaxy evolution, but the physics of the ubiquitous outflowing high velocity gas seen from rapidly star-forming galaxies remains unknown. I will describe a series of projects designed to shed light on these open questions, with a focus on how to produce cool atomic and warm photo-ionized gas at high velocities. One idea is to precipitate the cool gas from the super-heated hot phase on scales outside the host galaxy. Another option is to directly accelerate the cool gas from the galaxy with momentum injection, perhaps provided by radiation pressure on dust, cosmic rays, or a putative fast, hot wind. I'll highlight challenges on both the observational and theoretical fronts, and connect to observational constraints on physical scales ranging from the host galaxy's molecular clouds to its circumgalactic medium.

Jonathan Stern

  Jan. 30

Maxwell Moe
   University of Arizona
    How I Learned to Stop Worrying and Love Eclipsing Binaries

Wide-field photometric surveys have discovered hundreds of thousands of eclipsing binaries (EBs), and Gaia, TESS, and LSST will soon discover millions more. EBs provide the fundamental stellar relations and the most accurate distances to local group galaxies, and we are continuously finding new ways to utilize EBs as precise astrophysical tools. For example, collaborators and I developed a novel method for measuring the ages, masses, eccentricities, and dust extinctions of EBs based solely on their photometric light curves. By age-dating large samples of EBs, we have measured the acceleration of H II regions due to stellar feedback, calibrated the anti-correlation between dust extinction and age, found empirical evidence for an important tidal dissipation mechanism, and discovered a new class of nascent EBs with extreme mass ratios. I will discuss how the statistics of EBs provide stringent tests for models of protobinary fragmentation, accretion, and orbital migration. In addition, the updated multiplicity statistics serve as reliable initial conditions for binary population synthesis studies, revealing new insights into the progenitors of Type Ia supernovae, X-ray binaries, and sources of gravitational waves. I will end by highlighting the VARiability Survey of the TriAngulum GAlaxy (VARSTAGA), the first simultaneously deep and high-cadence survey of a local group galaxy specifically designed to discover unique classes of EBs, variables, and transients.

Diego Munoz

  Feb. 6

Heino Falcke
   Radboud University
    Imaging Black Holes Now and in the Future

One of the most fundamental predictions of general relativity are black holes. Their defining feature is the event horizon, the surface that even light cannot escape. So far, we have never seen the event horizon, but this is about to change. Advanced computer simulations make clear predictions of how the shadow of black holes should look like and global interferometric radio observations with the Event Horizon Telescope are now trying to image the supermassive black hole in the center of our own Milky Way and the radio galaxy M87 for the very first time. To improve the imaging quality further more telescopes should be added to the array, in particular in Africa. The more distant future will belong to higher frequencies and space-based interferometry. The talk will give an overview of the ongoing research to image and simulate black holes, as well as of plans for future expansions.

Rocco Coppejans

  Feb. 13

Rebekah (Bekki) Dawson
   Pennsylvania State University
    Origins of Super-Earths in Inner Solar Systems

Over the past decade, exoplanet surveys have discovered that many other solar systems teem with super-Earths on sub-Mercury orbits. A major open question is whether these super-Earths formed on their observed close-in orbits or formed at a wider separations and migrated in. I will present recent work on what the orbital and compositional properties of super-Earths in inner solar systems can reveal about super-Earths’ origins and more generally about the physical processes driving the formation and evolution of planetary systems.

Wen-fai Fong

  Feb. 20

Christina Williams
   University of Arizona
   The Emergence of Quenched Galaxies in the Era of JWST

The cessation of star-formation in galaxies remains poorly understood, despite being one of the most influential events in galaxy evolution. It is now known that high stellar mass density is strongly associated with this process at z~2-3, but the reason for this association is also poorly understood. Does high stellar density have a causal link with quenching, or is it a side effect of rapid growth in the early Universe? I will present new spectroscopic studies of stellar ages, molecular gas content, and feedback signatures that collectively provide evidence in favor of the latter scenario: compact galaxies grow fast in the first few billion years, but their high stellar density does not directly cause quenching. Understanding the early evolutionary development of the first quenched galaxies at z>3 is a major science goal of the James Webb Space Telescope (JWST), and I will discuss how future extragalactic surveys with this groundbreaking facility will resolve outstanding questions about their formation scenarios. In particular, I will talk about surveys that are planned as part of the Guaranteed Time Observations (GTO) and our predictions for the science results we expect from JWST Cycle 1.

Wen-fai Fong

  Feb. 27

Duncan Lorimer
   West Virginia University
   Fast Radio Bursts -- Nature's Latest Cosmic Mystery

Fast Radio Bursts are millisecond-duration pulses of unknown origin that were discovered by pulsar astronomers in 2007. A decade on from the discovery, with only 20 further bursts currently known, fast radio bursts remain enigmatic sources which parallel the early days of gamma-ray burst astronomy in the early 1970s. I will tell the story of their discovery, summarize what we know about them so far, describe the science opportunities these bursts present, and make predictions for what we will learn in the next decade.

Deanne Coppejans

  Mar. 6

Maria Drout
   Carnegie Institute for Science

Giacomo Terreran

  Mar. 13

Sasha Philippov
   UC Berkeley

Sasha Tchekhovskoy

Spring Quarter 2018

  Date      Speaker / Seminar Host
  Apr. 3

Shami Chatterjee
   Cornell University

Deanne Coppejans

  Apr. 24

Suvi Gezari
   University of Maryland

Giacomo Terreran

  May 1

Rachel Somerville
   Rutgers University

Sarah Wellons

  May 22

Charlie Conroy
   Harvard University

Cliff Johnson

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Past Astrophysics Seminars