Generation of Plasmas Around Spinning Black Holes*

Relativistic jets are ubiquitously observed in numerous systems with central black holes (BH) with a wide range of masses: from the stellar mass BH in microquasars to the supermassive BH in active galactic nuclei and quasars. These jets are thought to be powered by the Blandford-Znajek mechanism, which taps the spin energy of the BH into the EM Poynting flux. In order to operate, the entire region must be conductive, that is it must contain plasma. It the steady state regime, the plasma can only be replenished {\it in situ} via an electron-positron cascade. Here we first discuss the mechanism. Furthermore, we present the results of the numerical solutions of the appropriate equations and deduce interesting and important scaling relations between the plasma parameters, the output gamma-ray-power, mass of the central BH and the ambient radiation field from an accretion disk. Observational predictions are also made.