STATIONARY VERSUS NONSTATIONARY FORCE-FREE BLACK HOLE MAGNETOSPHERES

An axisymmetric, stationary, general-relativistic, electrodynamic engine model of an active galactic nucleus was formulated by Macdonald and Thorne, which consisted of a supermassive black hole surrounded by a plasma magnetosphere and a magnetized accretion disk. Based on this initial formulation, a nonstationary, force-free version of their model was constructed by Park and Vishniac, with the simplifying assumption that the poloidal component of the magnetic field line velocity be confined along the radial direction in cylindrical polar coordinates. In this paper, the equations for both the stationary and nonstationary cases are rederived in a clearer way.