Basic Properties of a Stationary Accretion Disk Surrounding a Black Hole

Abstract

The structure of a stationary accretion disk surrounding a blackhole is studied by means of newly developed basic equations. Thebasic equations are derived under the assumption that the verticaldistribution of disk matter is given by a polytrope. For a Keplerianaccretion disk, basic equations reduce to a differential equationof the first order. We have found that solutions of an opticallythick accretion disk converge to a limiting value, irrespective ofthe outer boundary condition. This gives the happy consequence thatthe inner structure of an optically thick accretion disk is determinedirrespective of the outer boundary condition. On the contrary, anoptically thin accretion disk shows bimodal behavior, that is, twophysically distinct states exist depending on the outer boundarycondition imposed at the outer edge of the accretion disk.