Electromagnetic extraction of energy from Kerr black holes

We elucidate the right' process for energy extraction from Kerr black holes through FFDE’ magnetospheres, free from causality violation. It is shown that the magnetosphere of a Kerr black hole possesses the double-structure, consisting of the inner and outer magnetospheres with the pair-creation gap between them and with respective unipolar batteries at the inner and outer surfaces of the gap.