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;