Publication date: Nov 2006
Abstract:
Perfect fluid tori with uniform distribution of the specific angular
momentum orbiting the Kerr-de Sitter black holes or naked singularities
are studied. Closed equipotential surfaces corresponding to stationary
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 due to the
violation of hydrostatic equilibrium. The repulsive cosmological
constant, Λ > 0, implies the existence of the outer cusp (with a
stabilizing effect on the tori because of excretion, i.e., outflow of
matter from the torus into the outer space) and the strong collimation
of open equipotential surfaces along the rotational axis. Both the
effects take place nearby so-called static radius where the
gravitational attraction is just balanced by the cosmic repulsion. 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
nonrelativistic adiabatic equation of state give limits on their central
mass-density, for which the approximation of test fluid is adequate.
Authors:
Stuchlík, Zdeněk; Slaný, Petr;