Astrophysics Science Division Colloquium Series
Schedule: Fall 2014

Astrophysics Science Division Colloquium Series
Schedule: Fall 2014

Recent schedules:

  2014, Spring  
2013, Fall 2013, Spring 2013, Summer
2012, Fall 2012, Spring  
2011, Fall 2011, Spring  
2010, Fall 2010, Spring  

ASD Colloquia are Tuesdays at 3:45 pm (Meet the Speaker at 3:30 pm)
in Bldg 34, Room W150 unless otherwise noted.


Aug 26 John ZuHone (GSFC) - The Physics of Gas Sloshing in the Cores of Galaxy Clusters


Sep 9 Emily Levesque (Colorado) - Discovery of a Thorne-Zytkow Object Candidate in the Small Magellanic Cloud
Sep 16 Kartik Sheth (NRAO) - Reconstructing the Mass Assembly of Galaxy Disks over the last 12 Billion Years with ALMA, HST and Spitzer
Host: Amber Straughn
Sep 23 Mario Livio (STScI) - Brilliant Blunders
Sep 30 Steve Boggs (Berkeley) -


Oct 7 David Merritt (RIT) -
Oct 21 Volker Bromm (UT Austin) - The First Stars and Galaxies: Run-up to the JWST
Oct 28 Iossif Papadakis (Crete) -


Nov 4 -
Nov 18 -
Nov 26 -


Dec 2 Jacqueline Hodge (NRAO) -
Dec 9 Mariska Kriek (Berkeley) -
Dec 16 Arash Bodaghee (GCSU) - Cold Exoplanets and Eccentric Rings

The Physics of Gas Sloshing in the Cores of Galaxy Clusters

John ZuHone


Tuesday, August 26, 2014


Many X-ray observations of relaxed galaxy clusters reveal the presence of sharp, spiral-shaped discontinuities in the surface brightness of the X-ray emitting gas. Spectral analysis of these features shows that the colder gas is on the brighter side, hence they have been dubbed "cold fronts." These features arise naturally in simulations from the cool-core gas "sloshing" in the gravitational potential. Their sharpness and stability has important implications for the microphysics of the ICM. The sloshing motions may have other effects, such as contributing to the heating of the cluster core and the acceleration of relativistic particles. I will present simulations of gas sloshing in clusters, explain their formation and evolution, and discuss the implications for the physics of the ICM, including fresh results on heat conduction, viscosity, and radio mini-halos.

Discovery of a Thorne-Zytkow Object Candidate in the Small Magellanic Cloud

Emily Levesque


Tuesday, September 9, 2014


Thorne-Zytkow objects (TZOs) are a theoretical class of star in which a compact neutron star is surrounded by a large, diffuse envelope. Supergiant TZOs are predicted to be almost identical in appearance to red supergiants (RSGs), with their very red colors and cool temperatures placing them at the Hayashi limit on the H-R diagram. The best features that can be used at present to distinguish TZOs from the general RSG population are the unusually strong heavy-element lines present in their spectra. These elements are the unique products of the star's fully convective envelope linking the photosphere with the extraordinarily hot burning region in the vicinity of the neutron star core. As part of a recent high-resolution spectroscopic search, my collaborators and I have discovered a TZO candidate in the Small Magellanic Cloud. It is the first star to display the distinctive chemical profile of anomalous element enhancements thought to be unique to TZOs. The positive detection of a TZO would provide the first direct evidence for a completely new model of stellar interiors, a theoretically predicted fate for massive binary systems, and never-before-seen nucleosynthesis processes that would offer a new channel for heavy-element production in our universe.

Reconstructing the Mass Assembly of Galaxy Disks over the last 12 Billion Years with ALMA, HST and Spitzer

Kartik Sheth


Tuesday, September 16, 2014


Bars are a key signpost in the evolutionary history of a disk galaxy. When a disk is sufficiently massive, dynamically cold and rotationally supported, and sufficient time has elapsed for the baryonic matter to exchange energy and angular momentum with the dark matter halo or the outer disk, the formation of a bar is inevitable. Therefore understanding the evolution of the bar fraction as a function of the host galaxy properties and as a function of redshift provides important clues to the evolutionary history of galaxies. I will present the latest results on local bars from the Spitzer Survey of Stellar Structure in Galaxies (S4G) and discuss the observations for the declining bar fraction with redshift from the COSMOS survey. A plausible reason for the decline in the bar fraction may be that galaxy disks were too dynamically hot to host bars at higher redshift which we have investigated using the DEEP2 / AEGIS data. Together these data are beginning to provide a coherent and consistent picture for the assembly history of disks on the Hubble sequence. The star formation in these disks is also now being understood with the latest results from ALMA. I will show the latest results on the cosmological evolution of the molecular gas content in a mass-selected sample of galaxies at three epochs, z=2.2, z=1, and z=0.3 and discuss planned Cycle 1 observations of the molecular gas environment in the prototypical barred spiral NGC 1097.

Brilliant Blunders

Mario Livio


Tuesday, September 23, 2014


Even the greatest scientists have made some serious blunders. "Brilliant Blunders" concerns the evolution of life on Earth, of the Earth itself, of stars, and of the universe as a whole. In this talk, I shall concentrate on and analyze major errors committed by such luminaries as Charles Darwin, Linus Pauling, and Albert Einstein. I will also scrutinize the various types of blunders and attempt to identify their causes. Most importantly, however, I'll argue that blunders are not only inevitable, but rather part and parcel of progress in science and other creative enterprises.

The First Stars and Galaxies: Run-up to the JWSTT

Volker Bromm

UT Austin

Tuesday, October 21, 2014


Cold Exoplanets and Eccentric Rings

Arash Bodaghee


Tuesday, December 16, 2014


The only way to find true Neptune analogs around other stars and study their orbits is to interpret images of debris disks, extrasolar analogs of the Kuiper belt. Crisp new HST and ALMA images of debris disks around nearby stars like Fomalhaut show narrow rings offset from the star. Surely these eccentric rings are dynamical signposts of exo-Neptunes, hidden or not so hidden, sculpting the rings. But new models of debris disks are changing our understanding of the exoplanet-debris disk connection. I'll describe SMACK, a new kind of debris disk model that tracks planetesimal collisions in 3D, and how these collisions confute our usual dynamical intuition about eccentric rings. Then I'll consider the possibility that many of these systems contain hidden amounts of gas. The "photoelectric instability" can sculpt rings in such disks with no need for planets at all.

Jeremy Schnittman
NASA Logo, National Aeronautics and Space Administration