ASD Colloquium Series - Fall 2019

ASD Colloquium Series - Fall 2019

The Astrophysics Science Division colloquia occur on Tuesdays at 3:45 pm, with an opportunity to meet the speaker at 3:30 pm, in building 34, room W150 (unless otherwise noted). Schedules from past colloquium seasons are available.

Contact: Knicole Colon


Aug 27 Special Location: Building 34, Room W120A/B
Charlie Conroy (Harvard University) - Assembling our Galaxy


Sep 03 No Colloquium
Sep 10 Marcelle Soares-Santos (Brandeis University) - Cosmology in the era of multi-messenger astronomy with gravitational waves
Sep 17 Special Location: Building 34, Room W120A/B
Jessica Werk (University of Washington) - A Colossal Galaxy Adventure
Sep 24 Matteo Cantiello (Flatiron Institute) - The New Era of Stellar Physics


Oct 01 Cara Battersby (University of Connecticut) - The Milky Way Laboratory
Oct 08 Special Location: Building 34, Room W120B
Davide Lazzati (Oregon State University) - Electromagnetic emission from binary neutron star mergers
Oct 15 Kirsten Hall (Johns Hopkins University) - Quantifying Quasar Wind Energy via the Sunyaev-Zel'dovich Effect
Oct 22 No Colloquium
Oct 29 Special Location: Building 34, Room W305
Jessie Christiansen (NASA Exoplanet Science Institute) - Ten Thousand Pieces of Blue Sky: Building towards the complete picture of exoplanet demographics


Nov 05 Special Location: Building 3 Auditorium
Erika Hamden (University of Arizona) - Why do galaxies look the way they do? The diffuse universe in ultraviolet
Nov 12 Kari Frank (Northwestern University) - A More Complete View of Supernova Remnants
Nov 19 Stephen Taylor (Vanderbilt University) - Pulsar Timing Arrays: The Next Frontier of Gravitational Wave Astronomy
Nov 26 No Colloquium - Thanksgiving Week


Dec 03 Ryan Trainor (Franklin and Marshall College) - Decoupling the Production and Escape of Lyman Photons
Dec 10 Michele Trenti (University of Melbourne) - The SkyHopper Space Telescope: Big Science with a Tiny Telescope

Assembling our Galaxy

Charlie Conroy

Harvard University

Tuesday, Aug 27, 2019


I will review ongoing work aimed at understanding when and how the major structural components of our Galaxy came into place. The combination of Gaia DR2 and spectroscopic data has revealed that the stellar halo contains a remarkable degree of structure, and appears to have formed partially by dynamical processes within the disk, and partially from accreted dwarf galaxies. Our simulations of the stellar disk predict that the clustered nature of star formation imprints a high degree of structure in phase+chemistry space. This structure is now being measured in the data, and promises to deliver new insights into the nature of star formation and the dynamical history of the disk.

Cosmology in the era of multi-messenger astronomy with gravitational waves

Marcelle Soares-Santos

Brandeis University

Tuesday, Sep 10, 2019


Motivated by the exciting prospect of a new wealth of information arising from the first observations of gravitational and electromagnetic radiation from the same astrophysical phenomena, the Dark Energy Survey (DES) has established a search and discovery program for the optical transients associated with LIGO/Virgo events (DESGW). Using the Dark Energy Camera (DECam), DESGW has contributed to the discovery of the optical transient associated with the neutron star merger GW170817, and produced the first cosmological measurements using gravitational wave events as standard sirens. We now pursue new results during the third, and ongoing, observing campaign. In this talk, I present an overview of our results, and discuss its implications for the emerging field of multi-messenger cosmology with gravitational waves and optical data.

A Colossal Galaxy Adventure

Jessica Werk

University of Washington

Tuesday, Sep 17, 2019


Most of the atomic matter in the Universe courses through the dark, vast spaces between galaxies. This diffuse gas cycles into and out of galaxies multiple times. It will form new stars and become swept up in violent stellar end-of-life processes. Astronomers believe that this gaseous cycle lies at the heart of galaxy evolution. Yet, it has been difficult to observe directly. Owing to the vastly improved capabilities in space-based UV spectroscopy with the installation of the Cosmic Origins Spectrograph on the Hubble Space Telescope, observations and simulations of this diffuse material have emerged at the frontier of galaxy evolution studies. In the last decade, we have learned that Milky Way mass galaxies harbor enough material outside of their visible disks to sustain star-formation for billions of years. Remarkably, our observations indicate that most of the heavy elements on earth cycled back and forth multiple times through the Milky Way’s extended halo before the formation of the solar system. In the spirit of MS-DOS adventure games, I have designed a fully interactive colloquium that operates on a complex network of powerpoint hyperlinks. In this adventure, you will choose any of 36 possible tracks on which to explore observational and simulated signatures of cosmic gas flows.

The New Era of Stellar Physics

Matteo Cantiello

Flatiron Institute

Tuesday, Sep 24, 2019


Stellar astrophysics is undergoing a renaissance driven by new observational and theoretical capabilities. Wide-field time-domain surveys have uncovered new classes of stellar explosions, helping to understand how stars evolve and end their lives. Gravitational-wave astronomy is providing exciting insights in the properties of the final remnants of massive stars. Asteroseismology, the study of waves in stars, is also producing dramatic breakthroughs in stellar structure and evolution. Thanks to space astrometry, accurate distances are now available for an unprecedented number of galactic stars.

From the theoretical standpoint, it is increasingly possible to study aspects of the three-dimensional structure of stars using targeted numerical simulations. These studies can then be used to develop more accurate models of these physics in one-dimensional stellar evolution codes. I will review some of the most important results in stellar physics of the last few years, and highlight what are the most relevant puzzles that still need to be solved. I will put particular emphasis on the physics of massive stars, which are the progenitors of core-collapse supernovae, gamma-ray bursts and the massive compact remnants observed by LIGO.

The Milky Way Laboratory

Cara Battersby

University of Connecticut

Tuesday, Oct 01, 2019


Our own Milky Way Galaxy is a powerful and relatively nearby laboratory in which to study the physical processes that occur throughout the Universe. From the organization of gas on galactic scales to the life cycle of gas and stars under varied environmental conditions, studies of our Milky Way underpin many areas of modern astrophysics. I will present a brief tour of our Milky Way Laboratory, including 1) the connection between long, filamentary molecular clouds and spiral structure, and 2) how observing our extreme, turbulent Galactic Center (the Central Molecular Zone) can help us learn more about how gas is converted into stars during the peak epoch of cosmic star formation. I will also briefly discuss the Origins Space Telescope, a NASA mission concept study for the 2020 Decadal survey, opening up about 3 orders of magnitude of discovery space on science from first stars to life.

Electromagnetic emission from binary neutron star mergers

Davide Lazzati

Oregon State University

Tuesday, Oct 08, 2019


The detection of gravitational waves, gamma-rays, and multi wavelength radiation from the binary neutron star merger GW170817 has been an enormous breakthrough in astrophysics. It has confirmed some theoretical expectations and opened new riddles. I will extensively introduce the observations and physics of the event and then concentrate on the non-thermal component of the emission and on the possible the association of binary neutron star mergers with short-duration gamma-ray bursts. I will show that the most likely scenario is the one in which GW170817 produced a canonical short gamma-ray burst jet that was misaligned with our line of sight, resulting in unusual behavior. I will finally discuss the results of the O3 observation period of LIGO and what to expect from the future.

Quantifying Quasar Wind Energy via the Sunyaev-Zel'dovich Effect

Kirsten Hall

Johns Hopkins University

Tuesday, Oct 15, 2019


Accreting supermassive black holes impact the evolution of massive galaxies via quasar-driven winds and other forms of feedback. One firm prediction of quasar feedback models is a hot bubble of post-shock gas, which can be observed via the thermal Sunyaev-Zel’dovich (tSZ) effect in the millimeter regime of quasar spectral energy distributions (SEDs). I will present the average SEDs of 109,829 optically-selected, radio quiet quasars from 1.4~GHz to 3000~GHz in six redshift bins between 0.3<z<3.5. We model the emission components in the radio and far-infrared, plus a spectral distortion from the tSZ effect. If the measured tSZ effect is primarily due to hot bubbles from quasar-driven winds, we find that (5.0 +/- 1.3)% of the quasar bolometric luminosity couples to the intergalactic medium over a fiducial quasar lifetime of 100 Myr. I will discuss other possible sources of the tSZ signal in quasar environments as well as our measurement of excess millimeter emission in quasar SEDs at z<1.91.

Ten Thousand Pieces of Blue Sky: Building towards the complete picture of exoplanet demographics

Jessie Christiansen

NASA Exoplanet Science Institute

Tuesday, Oct 29, 2019


The NASA Kepler mission has provided its final planet candidate catalogue, the K2 mission has contributed another four years’ worth of data, and the NASA TESS mission has just started producing planet candidates of its own. The demographics of the exoplanet systems probed by these transiting exoplanet missions are complemented by the demographics probed by other techniques, including radial velocity, microlensing, and direct imaging. I will walk through the progress of the Kepler occurrence rate calculations, including some of the outstanding issues that are being tackled. I will present some new results from K2, and outline how K2 and TESS will able to push the stellar parameter space in which we can explore occurrence rates beyond that examined by Kepler. Finally, I will highlight some of the pieces of the larger demographics puzzle - occurrence rate results from the other techniques that probe different stellar and exoplanet regimes - and how we can start joining those pieces together.

Why do galaxies look the way they do? The diffuse universe in ultraviolet

Erika Hamden

University of Arizona

Tuesday, Nov 05, 2019


My interest in astrophysics focuses on answering a seemingly simple question- why do galaxies look the way they do? My work as a telescope and instrument builder is driven by observing light from faint, diffuse hydrogen to try to answer that question. I will discuss my work in ultraviolet technology and instrument development (delta-doped UV detectors, the FIREBall-2 mission, and others) in the context of making difficult observations of some of the faint parts of the circumgalactic medium. I will also describe how important technology development is to our understanding of the universe, and how much failure plays a role in all of science.

A More Complete View of Supernova Remnants

Kari Frank

Northwestern University

Tuesday, Nov 12, 2019


Supernova remnants (SNRs) are complex, three-dimensional objects; properly accounting for this complexity when modeling the resulting X-ray emission presents quite a challenge and makes it difficult to accurately characterize the properties of the full SNR volume. The SPIES (Smoothed Particle Inference Exploration of Supernova remnants) project aims to address this challenge by applying a fundamentally different approach to analyzing X-ray observations of SNRs. Smoothed Particle Inference is a Bayesian modeling process that fits a population of gas blobs ("smoothed particles") such that their superposed emission reproduces the observed spatial and spectral distribution of photons. I will present the results of applying this new approach to the SNRs DEM L71 and W49B.

Pulsar Timing Arrays: The Next Frontier of Gravitational Wave Astronomy

Stephen Taylor

Vanderbilt University

Tuesday, Nov 19, 2019


Gravitational-wave detectors are yielding a bounty of observations, and revolutionising our understanding of stellar-mass black holes. But what about the supermassive black holes that lurk at the heart of massive galaxies? These titans form binaries over cosmic time as a byproduct of hierarchical galaxy growth, emanating gravitational waves in the nanohertz sensitivity band of networks of Milky Way millisecond pulsars. Pulsar-timing arrays (PTAs) like the North American Nanohertz Observatory for Gravitational waves (NANOGrav) are poised to chart this new frontier of gravitational wave discovery within the next several years. With this new window onto the warped Universe, PTAs will bring a sea-change in our understanding of supermassive binary black-hole demographics and dynamical interactions. Combined with electromagnetic signatures of binary AGN in upcoming time-domain synoptic surveys, PTAs will extend the arena of multi-messenger astronomy to the most massive black holes in the Universe. Additionally, pulsar-timing arrays are currently placing compelling constraints on modified gravity theories, cosmic strings, and ultralight scalar-field dark matter. I will review the current status of PTA searches, and present some milestones on the road to the exciting next decade and beyond of PTA discovery.

Decoupling the Production and Escape of Lyman Photons

Ryan Trainor

Franklin and Marshall College

Tuesday, Dec 03, 2019


Ultraviolet Lyman-alpha and Lyman-continuum photons couple strongly to neutral hydrogen, and these processes shape the observability of galaxies as well as their effects on their surrounding media. However, the measured Lyman emission of a given galaxy is challenging to interpret. Lyman photons are produced within star-forming regions, but the observed emission also depends on the scattering and absorption of these photons on much larger scales. I will present results from the Keck Baryonic Structure Survey of more than 1000 galaxies at z=2-3 that are allowing us to empirically study the relationships between observed Lyman-alpha and Lyman-continuum emission and many different physical properties of galaxies. I will discuss how these observations allow us to separate the physics of photon production from that of photon escape, and what these relationships tell us about galaxy selection, stellar feedback, and the role of star-forming galaxies in reionization.

The SkyHopper Space Telescope: Big Science with a Tiny Telescope

Michele Trenti

University of Melbourne

Tuesday, Dec 10, 2019


Orbiting telescopes, large or small, have been so far primarily confined to complex missions run by government agencies. However, thanks to dramatic technological improvements, CubeSats (nano-satellites based on standardised dimensions) are now offering new scientific opportunities. In this talk I will review the status of the field and discuss how observations from space will advance astronomy in the next decade. Within this context, I'll introduce the SkyHopper mission concept, a 12U (~21kg) CubeSat with a 15cm-aperture infrared space telescope being designed in Australia for a 2023 launch. SkyHopper will carry an actively-cooled four-channel camera covering the spectral range from 0.8 to 1.7 micron simultaneously, and be capable of re-pointing to new targets within two minutes thanks to satellite phone network communications and rapid slew. The combination of timeliness on target and low-noise infrared image quality from space will offer a facility unique in the world to complement larger missions in multiple areas of astronomy such as TESS and Swift. In particular, SkyHopper will contribute to the discovery of potentially habitable Earth-size planets around nearby cool stars and to the prompt characterisation of the photometric redshift of gamma ray burst afterglows generated by the explosion of massive stars out to the edge of the observable Universe.

Past Colloqia Schedules

2019: Fall, Spring
2018: Fall, Spring
2017: Fall, Spring
2016: Fall, Spring
2015: Fall, Spring
2014: Fall, Spring
2013: Fall, Spring, Summer
2012: Fall, Spring
2011: Fall, Spring
2010: Fall, Spring

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