Electromagnetic energy for a charged Kerr black hole in a uniform magneticfield - art. no. 084033

With the Komar mass formula we calculate the electromagnetic energy for a c harged Kerr black hole in a uniform magnetic field. We find that the total electromagnetic energy takes the minimum when the Kerr black hole possesses a nonzero net charge Q=2 xi B(0)J(H) where B-0 is the strength of the magn etic field, J(H) is the angular momentum of the black hole, and xi is a dim ensionless parameter determined by the spin of the black hole. However, the Wald state with Q = 2B(0)J(H) does not minimize the electromagnetic energy .