Speaker
Description
Whether a rotating black hole in an external magnetic field actually charges up to the theoretical Wald value has remained an open question with major implications for magnetospheric structure and particle acceleration. Using general-relativistic particle-in-cell simulations with self-consistent pair production, we evolve black holes of different spins from two opposite starting charges and find that both converge to the same steady-state value within a few tens of gravitational times, showing the equilibrium is a true dynamical attractor rather than a relic of initial conditions. This equilibrium charge sits well below the Wald prediction — around 30% of it for moderate spins, dropping toward zero as the spin approaches its maximum value. We show this behavior matches a simple analytic formula derived by balancing the magnetic flux carried by positive and negative charges through the horizon, confirming that charge transport along field lines governs the result. The findings establish that a black hole's charge state is set by kinetic plasma physics rather than the Wald formula alone, and that since the equilibrium charge remains below the Wald value, it does not shut down the potential drop that powers energy-extraction mechanisms like Blandford-Znajek.