Evolution of a Rotating Black Hole with a Magnetized Accretion Disk

The effect of an accretion disk on the Blandford-Znajek process and the evolution of a black hole are discussed using a simplified system for the black hole - accretion disk in which the accretion rate is supposed to be dominated by the strong magnetic field on the disk. The evolutions of the mass and the angular momentum of the black hole are formulated and discussed with numerical calculations.