"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.
"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.
"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.
"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.