Accretion of Gas onto Black Holes

Abstract

We outline the phenomena associated with accreting black holes. At the beginning a spherical symmetric accretion is considered. Probably the most important physical phenomenon which leads to observational manifestation of a black hole presence is a disk gas accretion. We discussed some aspects of the disk accretion. Accretion disk theory was first developed with local heat balance, where the whole energy produced by a viscous heating was emitted to the sides of the disk. One of the most important invention of this theory was a phenomenological treatment of the turbulent viscosity, known as “alpha” prescription, when the [r ϕ] component of the stress tensor was approximated by [α P] where P is pressure and α is an unknown constant. In parallel to the optically thick geometrically thin accretion disk models, a new branch of the optically thin accretion disk models was discovered, with a larger thickness for the same total luminosity. The choice between these solutions should be done on the base of a stability analysis. The ideas underlying the necessity to include advection are reviewed. The present status of the solution for a low-luminous optically thin accretion disk model with advection is discussed and the limits for an advection dominated accretion flows [ADAF] imposed by the presence of magnetic field are analyzed.