Quantum Electrodynamical Effects in Kerr-Newmann Geometries

Following the classical approach of Sauter, of Heisenberg and Euler and of Schwinger, the process of vacuum polarization in the field of a ''bare'' Kerr-- Newman geometry is studied. The value of the critical strength of the electromagnetic fields is given together with an analysis of the feedback of the discharge on the geometry. The relevance of this analysis for current astrophysical observations is mentioned.