**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;