  Black holes are known to launch powerful relativistic jets and emit highly
variable gamma radiation. How these jets are loaded with plasma remains poorly
understood. Spark gaps are thought to drive particle acceleration and pair
creation in the black-hole magnetosphere. In this paper, we perform 2D
axisymmetric general-relativistic particle-in-cell simulations of a monopole
black-hole magnetosphere with a realistic treatment of inverse Compton
scattering and pair production. We find that the magnetosphere can
self-consistently fill itself with plasma and activate the Blandford-Znajek
mechanism. A highly time-dependent spark gap opens near the inner light surface
which injects pair plasma into the magnetosphere. These results may account for
the high-energy activity observed in active galactic nuclei and explain the
origin of plasma at the base of the jet.
