APT1 - Astrophysical Black Holes |
Speaker_ |
Slany, Petr |
Co-autors |
Zdenek Stuchlik |
Talk _ |
Marginally stable thick discs orbiting Kerr--de Sitter black holes |
Abstract _ |
Perfect fluid tori with uniform distribution of the specific angular momentum orbiting KdS black holes or naked singularities are studied. Toroidal discs are allowed only in the spacetimes admitting stable circular geodesics.The last closed surface crosses itself in the cusp(s) enabling outflow(s) of matter from the torus. The repulsive (positive) cosmological constant implies existence of the outer cusp (with a stabilizing effect on the tori because of excretion) and strong collimation of open equipotential surfaces along the rotational axis. The plus-family discs, which are always corotating in the black-hole backgrounds but can be counterrotating, even with negative energy of the fluid elements, in some naked-singularity backgrounds, are thicker and more extended than the minus-family ones (which are always counterrotating in all backgrounds). If parameters of the naked-singularity spacetimes are very close to the parameters of extreme black-hole spacetimes, the family of possible disc-like configurations includes members with two isolated discs where the inner one is always a counterrotating accretion disc. Mass estimates for tori with adiabatic equation of state give limits on their central mass-density, for which the approximation of test fluid is adequate. |