**Publication date:** Nov 2000

**Abstract:**

The hydrodynamical structure of perfect fluid orbiting Schwarzschild-de

Sitter black holes is investigated for configurations with uniform

distribution of angular momentum density. It is shown that in the

black-hole backgrounds admitting the existence of stable circular

geodesics, closed equipotential surfaces with a cusp, allowing the

existence of toroidal accretion disks, can exist. Two surfaces with a

cusp exist for the angular momentum density smaller than the one

corresponding to marginally bound circular geodesics; the equipotential

surface corresponding to the marginally bound circular orbit has just

two cusps. The outer cusp is located nearby the static radius where the

gravitational attraction is compensated by the cosmological repulsion.

Therefore, due to the presence of a repulsive cosmological constant, the

outflow from thick accretion disks can be driven by the same mechanism

as the accretion onto the black hole. Moreover, properties of open

equipotential surfaces in vicinity of the axis of rotation suggest a

strong collimation effects of the repulsive cosmological constant acting

on jets produced by the accretion disks.

**Authors:**

Stuchlík, Z.; Slaný, P.; Hledík, S.;