Publication date: Sep 2005
Abstract:
Perfect fluid tori with a uniform distribution of the specific angular
momentum, ell(r, θ) = const, orbiting the Kerr de Sitter black holes or
naked singularities are studied. It is well known that the structure of
equipotential surfaces of such marginally stable tori reflects the basic
properties of any tori with a general distribution of the specific
angular momentum. Closed equipotential surfaces corresponding to
stationary thick discs are allowed only in the spacetimes admitting
stable circular geodesics. The last closed surface crosses itself in the
cusp(s) enabling the outflow of matter from the torus due to the
violation of hydrostatic equilibrium. The inner cusp enables an
accretion onto the central object. The influence of the repulsive
cosmological constant, Λ > 0, on the equipotential surfaces lies in
the existence of the outer cusp (with a stabilizing effect on the thick
discs) and in the strong collimation of open equipotential surfaces
along the rotational axis. Both the effects take place near a so-called
static radius where the gravitational attraction is just balanced by the
cosmic repulsion. The outer cusp enables excretion, i.e., the outflow of
matter from the torus into the outer space. The plus-family discs (which
are always co-rotating in the black-hole backgrounds but can be counter-
rotating, 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 counter-rotating in all
backgrounds). For co-rotating discs in the naked-singularity spacetimes,
the potential well between the centre of the disc and its edges at the
cusps is usually much higher than in the black-hole spacetimes. If the
parameters of 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 counter-rotating accretion disc.
Authors:
Slaný, Petr; Stuchlík, Zdenek;