Two-dimensional Particle-in-cell Simulations of Axisymmetric Black Hole Magnetospheres

We investigate the temporal evolution of an axisymmetric magnetosphere around a rapidly rotating stellar-mass black hole by applying a two-dimensional particle-in-cell simulation scheme. Adopting homogeneous pair production and assuming that the mass accretion rate is much less than the Eddington limit, we find that the black hole's rotational energy is preferentially extracted from the middle latitudes and that this outward energy flux exhibits an enhancement that lasts approximately 160 dynamical timescales. It is demonstrated that the magnetohydrodynamic approximations cannot be justified in such a magnetically dominated magnetosphere because Ohm's law completely breaks down and the charge-separated electron-positron plasmas are highly nonneutral. An implication is given regarding the collimation of relativistic jets.