Feb 25

"The Physics of Gas Sloshing in the Cores of Galaxy Clusters"
John ZuHone, NASA/Goddard Space Flight Center

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 as sloshing in clusters, explain their formation and evolution, and discuss the implications for the physics of the ICM, including fresh results on heat conduction and radio mini-halos.

Mar 18

"The Bosma Effect: Why is the ISM a dynamical tracer of DM?"
Frederic V. Hessman, Georg-August-Universitat Gottingen

One of the strangest baryonic-DM correlations is the Bosma Effect: the dynamic signature of DM in the rotation curves of spiral galaxies is directly proportional to that of the ISM. Recently, it has been proposed that this effect is caused by the way the ISM surface density and the amount of star formation is balanced through the epicyclic frequency of the disk and hence the rotation curve. I show that this idea is based upon a too unrealistic model of galaxies and much too loose interpretation of the data. A more realistic model for spiral galaxies generically fails to show this effect when tested using either a simple ISM instability model or one in which the stability of a star-gas system is considered. The alternative of a significant baryonic "dark disk" component is not as unthinkable as is commonly assumed, both observationally and theoretically.

Apr 1

"Theoretical Studies of Superluminous Supernovae"
Manos Chatzopoulos, University of Texas at Austin (PhD Defense Presentation: 3PM)

The past decade Texas astronomers discovered the brightest supernovae ever observed, the so called Superluminous Supernovae. Significant progress has been made ever since in understanding the nature and origin of these exceptional manifestations of violent stellar death. I will summarize the theoretical advances we have done here in UT Astronomy in understanding the nature of these events and their explosion mechanisms. These advances involved the development of analytical models that fit the light evolution from these events as well as sophisticated numerical simulations performed in the Texas Advanced Computing Center Ranger and Stampede supercomputers.

Apr 8

"Profiling Massive Black Holes through Stellar Tidal Disruption"
Enrico Ramirez-Ruiz, University of California, Santa Cruz

A star interacting with a massive black hole cannot be treated as a point mass if its gets o close to the black hole that it becomes vulnerable to tidal distortions and even disruption. When a rapidly changing tidal force starts to compete with a star's self-gravity, the material of the star responds on a complicated way. This phenomenon poses an as yet unmet challenge to computer simulations. The art of modeling the tidal disruption of stars by massive black holes forms the main theme of my talk. Detailed simulations should tell us what happen when stars of different types get tidally disrupted, and what radiation a distant observer might detect as the observational signature of such events.