Winds from Event Horizon Magnetospheres

Abstract

In this chapter we consider paired wind solutions driven by ergospheric dynamos on flux tubes that thread the event horizon. This is a more complicated flow problem than the ergospheric disk magnetosphere, since the flux tubes are doubly open ended (see Fig. 9.1). We showed in Chap. 6, in explicit detail, how there can be no meaningful MHD boundary condition near the horizon. The event horizon is completely describable in terms of an MHD asymptotic infinity. Thus, we no longer have the ergospheric disk or any boundary conditions that fix the field line angular velocity. There is no “solid” surface to anchor the magnetic flux tubes that thread the empty vacuum spacetime of the horizon. These are free floating magnetic flux tubes and the determination of the field line angular velocity is far from trivial. Thus, Ω _F can be estimated only by utilizing a deep understanding of the GHM causality of ergospheric dynamos as described in Chap. 7 and elucidated by the example of Chap. 8.