arXiv subjects

D. Vokrouhlicky

Publications and source records attributed to D. Vokrouhlicky.

22 records · Page 2Linked to original sources

arXiv1998

Stellar dynamics in a galactic centre surrounded by a massive accretion disc. I. Newtonian description

The long-term evolution of stellar orbits bound to a massive centre is studied in order to understand the cores of star clusters in central regions of galaxies. Stellar trajectories undergo tiny perturbation, the origin of which is twofold: (i) gravitational field of a thin gaseous disc surrounding the galactic centre, and (ii) cumulative drag due to successive interactions of the stars with material of the disc. Both effects are closely related because they depend on the total mass of the disc, assumed to be a small fraction of the central mass. It is shown that, in contrast to previous works, most of the retrograde (with respect to the disc) orbits are captured by the central object, presumably a massive black hole. Initially prograde orbits are also affected, so that statistical properties of the central star cluster in quasi-equilibrium may differ significantly from those deduced in previous analyses.

astro-ph↗

arXiv1997

Stellar capture by an accretion disc

Long-term evolution of a stellar orbit captured by a massive galactic center via successive interactions with an accretion disc has been examined. An analytical solution describing evolution of the stellar orbital parameters during the initial stage of the capture was found. Our results are applicable to thin Keplerian discs with an arbitrary radial distribution of density and rather general prescription for the star-disc interaction. Temporal evolution is given in the form of quadrature which can be carried out numerically.

astro-ph↗

arXiv1994

Emission Line Profiles from Self-Gravitating Thin Disks

We have constructed general relativistic models of a stationary, axially symmnetric, Keplerian thin disk around a rotating black hole. We computed profiles of a spectral line, emitted in the inner region of the disk. In our models we have taken into account also the self-gravity of the disk. The aim of this work is to study gravitational effects on the line profiles in connection with the X-ray features observed in spectra of active galactic nuclei. In some cases, the calculated profiles are clearly affected by the disk gravity but relativistic dragging effects are found to be negligible.

astro-ph↗

arXiv1993

Motion of a Solar Mass Compact Object Around a Massive Rotating Black Hole

This preprint is based on two articles accepted by MNRAS and ApJ. Our aim is to study the evolution of the orbit of a star under the influence of interactions with an accretion disc in an AGN. The model considered consists of a low-mass compact object orbiting a supermassive black hole and colliding periodically with the accretion disc. Gravitational field of the nucleus is described by the Kerr metric. The star is assumed to move along a geodesic arc between successive interactions with an equatorial accretion disc. We study the gravitomagnetic (Lense-Thirring) precession of the trajectory. We do not assume any particular value for the eccentricity or inclination of the orbit or the angular momentum of the black hole. We also discuss the periodicity related to the relativistic shift of the pericenter. The model of star-disc interactions has been suggested to explain the X-ray variability observed in the Seyfert galaxy NGC~6814. We briefly discuss on this subject.

astro-ph↗