  Black holes drive powerful plasma jets to relativistic velocities. This
plasma should be collisionless, and self-consistently supplied by pair creation
near the horizon. We present general-relativistic collisionless plasma
simulations of Kerr-black-hole magnetospheres which begin from vacuum, inject
electron-positron pairs based on local unscreened electric fields, and reach
steady states with electromagnetically powered Blandford-Znajek jets and
persistent current sheets. Particles with negative energy-at-infinity are a
general feature, and can contribute significantly to black-hole
rotational-energy extraction in a variant of the Penrose process. The generated
plasma distribution depends on the pair-creation environment, and we describe
two distinct realizations of the force-free electrodynamic solution. This
sensitivity suggests that plasma kinetics will be useful in interpreting future
horizon-resolving submillimeter and infrared observations.
