In 1975, following the work on the energetics of black holes, Damour and Ruffini pointed out the existence of the vacuum polarization process à là Sauter–Heisenberg–Euler–Schwinger around black holes endowed with electromagnetic structure (EMBHs), whose electric field strength exceeds the Schwinger critical value Ec = m 2 e c e~ , where c is the speed of light, e and me are electron charge and ...