Lecture Day: Annual reports from the Center for Theoretical Astrophysics 2011
SoÅˆa EhlerovÃ¡: Fragmented walls of the Carina Flare Supershell
CO observations of the molecular cloud in the wall of the Carina Flare Supershell made with the APEX telescope are presented. Clumps in the cloud are identified and interpreted as results of the gravitational fragmentation process in the shell, which is also affected by the pressure of the ambient medium. The mass spectrum of identified clumps is compared to theoretical predictions.
Petr Hadrava: Evolution of First Stars with Mass-loss
The first stars or the so called Population III stars were formed from the matter with primordial chemical composition determined by the conditions in the early universe, i. e. with extremely low content of heavy elements. It is supposed that the first stars had mostly very high masses and hence large luminosities and short evolution time-scale. Their radiation caused re-ionization of the universe and their remnants enriched the universe by heavy elements. However, this process depends on the form and rate of mass-loss by these stars which can take place already during their evolution before the final collapse. To investigate the role of this process, we have computed models of first-stars' evolution with parameterized mass-loss.
Ladislav Å ubr: Dynamical evolution of the young stellar disc in the Galactic center
Origin of several hundreds of young stars in within the distance $\lesssim 1\,\pc$ from the Galactic supermassive black hole still represents an open problem of contemporary astrophysics. In this contribution we further investigate the model which assumes their formation in-situ via fragmentation of a self-gravitating gaseous disc. We show that currently observed configuration of the system of young stars can be obtained an outcome of a dynamical evolution of a single, initially very thin stellar disc. Our model assumes the long-term evolution of the stellar disc to be determined by gravitational influence of a distant molecular torus (CND) and mutual resonances of stellar orbits within the disc.
Michal Bursa: Modeling thermal spectra of accretion disks
Accurate theoretical modeling of accretion disk spectra and their comparison with observation data provides an important technique for getting a better understanding of processes playing role in accretion disks driven by strong gravity. At the same time we can not only test how good are our theoretical models, but we can also probe properties of the disk's central engines - black holes.
Filiberto Hueyotl-Zahuantitla: Formation of the AGN torus in a nuclear starburst environment
I will present a model for the formation of the torus in active galactic nuclei from the matter reinserted by a rotating young nuclear star cluster (NSC). A necessary condition to form the torus is that the NSC must be in a catastrophic cooling regime. By using typical parameters of NSCs (mass, size, etc,... ) and black holes (BHs) in Seyfert galaxies, the model predicts dimensions of the torus as those inferred from observations. A simple analytic formula to estimate the radius of the torus in terms of the parameters of the NSC and BH will be presented.
David KofroÅˆ: The radiation properties of the C-metric
By casting the charged C-metric in the global boost-rotation symmetric form we are able to investigate its radiation properties in more details. This is a complicated task, and, unfortunately not yet completely done, as we are dealing with the gravitational radiation of an extended body, not only of a point-like particle. Also the gravitational-electromagnetic interaction is involved.
JiÅ™Ã KovÃ¡Å™: Charged perfect fluid structures near compact objects
Following our previous studies of charged test particles and uncharged perfect fluid tori encircling compact objects, we introduce here a simple test model of a charged perfect fluid torus in strong gravitational and electromagnetic fields. In contrast to ideal magnetohydrodynamic models, we consider here the opposite limit of negligible conductivity, where the charges are tied completely to the moving matter. To clearly demonstrate features of our model, we present three-dimensional axisymmetric charged toroidal configurations around Reissner-Nordstroem black holes and compare them with equivalent configurations of electrically neutral tori. The details of the study can be found in Kovar et al. (2011, Physical Review D, 84, 084002). Next, we describe an ongoing work on the Newtonian version of our model, which is, due to its simplicity, very suitable to illustrate the basic properties of the system. The Newtonian approach allows us to find the off-equatorial structures. These represent a generalization of our recent studies of the off-equatorial halo motion of charged test particles.
Martin Urbanec: Rotating compact stars
We will present results of compact star modeling based on Hartle-Thorne approach assuming matter being described by standard equations of state for neutron star matter and also equation of state describing the so called strange matter. Typical differences between neutron and strange star properties will be demonstrated. We will show implications on the astrophysical phenomena in the vicinity of these objects and how models of these phenomena could be tested using our models.