Time-dependent analysis of spherical accretion on to black holes

Results are presented from a time-dependent, numerical investigation of spherical accretion on to 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 about 10(3)-10(4) Schwarzschild radii, where Compton heating exceeds radiative cooling. The calculations have been 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.