Equilibrium configurations of perfect fluid orbiting Schwarzschild-de Sitter black holes

The hydrodynamical structure of perfect fluid orbiting Schwarzschild-de Sit ter black holes is investigated for configurations with uniform distributio n of angular momentum density. It is shown that in the black-hole backgroun ds admitting the existence of stable circular geodesics, closed equipotenti al surfaces with a cusp, allowing the existence of toroidal accretion disks , can exist. Two surfaces with a cusp exist for the angular momentum densit y 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 radiu s where the gravitational attraction is compensated by the cosmological rep ulsion. Therefore, due to the presence of a repulsive cosmological constant , the outflow from thick accretion disks can be driven by the same mechanis m as the accretion onto the black hole. Moreover, properties of open equipo tential surfaces in vicinity of the axis of rotation suggest a strong colli mation effects of the repulsive cosmological constant acting on jets produc ed by the accretion disks.