  This Letter investigates the physics that is responsible for creating the
current system that supports the outgoing Poynting flux emanating from the
ergosphere of a rotating black hole in the limit that the magnetic energy
density greatly exceeds the plasma rest mass density (magnetically dominated
limit). The underlying physics is derived from published three-dimensional
simulations that obey the general relativistic equations of perfect
magnetohydrodynamics (MHD). It is found that the majority of the Poynting flux
emitted from the magnetically dominated regions of the ergosphere has a source
associated with inertial effects outside of the event horizon.
