Accretion processes in black-hole spacetimes with a repulsive cosmological constant

The influence of a repulsive cosmological constant on accretion processes onto black holes is discussed. The steady, spherically symmetric adiabatic inflow and outflow of perfect fluid is considered. Further, the attention is focused on the properties of both geometrically thin, Keplerian accretion disks and geometrically thick, toroidal disks having relevant pressure gradients. It is shown that nearby the static radius, where the gravitational attraction of a black hole is just balanced by the cosmological repulsion, the accretion toroidal disks have an outer cusp enabling outflow of matter from the disk. Behind the static radius the cosmological repulsion efficiently collimates jets that emanate along the rotation axis of the toroidal disk.