Numerical simulation of thick disc accretion on to a rotating black hole

Abstract

We study two-dimensional axisymmetric accretion on to a rotating black hole by time-dependent fully relativistic hydro dynamical calculations. We investigate the innermost part of geometrically thick discs, in which most of the gravitationally released energy is advected into the black hole. Relativistic effects are important close to the cusp-like inner edge of the disc, where accretion proceeds with approximately constant angular momentum and the viscous time-scale exceeds the dynamical time-scale of accretion. We use the perfect fluid approximation and calculate isentropic flows with constant angular momentum. We confirm the previous analytical result that the structure of the innermost disc region strongly depends on the black hole spin. We find the mass accretion rate M to be in a good agreement with the analytical dependenceM oc (dW)rJ(r-I), where dWis the energy gap and r is the adiabatic index.