Time–dependent analysis of spherical accretion onto black holes

Results are presented from a time–dependent, numerical investigation of spherical accretion onto black holes, within the framework of relativistic radiation hydrodynamics. We have studied the stability of self–consistent, stationary solutions of black hole accretion with respect to thermal and radiative perturbations and also the non– linear evolution of unstable, high temperature models, heated by the hard radiation produced by the accretion flow itself in the inner region near to the horizon. In some cases, a hydrodynamic shock forms at around 10–10 Schwarzschild radii, where Compton heating exceeds radiative cooling. The calculations were made using a suitably designed radiation hydrodynamics code, in which radiative transfer is handled by means of the PSTF moment formalism and which contains an original treatment of the radiation temperature equation.