http://arxiv.org/abs/2108.08161
Recently, it was claimed that accretion of electric charge by a black hold rotating in an aligned external magnetic field results in a “dead” vacuum magnetosphere, where the electric field is totally screened, no vacuum breakdown is possible, and the Blandford-Znajek mechanism cannot operate (King & Pringle 2021). Here we study in details the properties of the Wald solution for electrically charged black holes which was considered in that paper. Our results show that the claim is erroneous as in this solution there exists a drop of electrostatic potential along all magnetic field lines except the one coinciding with the symmetry axis. It is also found that in contrast to the Meissner effect of uncharged black holes, charged black holes can pull magnetic field lines onto their event horizon, just like this was observed in some previous force-free and PIC simulations of black hole magnetospheres. This suggests that accretion of electric charge may indeed be a feature of the black hole electrodynamics. It is also shown that, the magnetospheric electric field cannot be screened even in the more general problem of a steady-state axisymmetric magnetosphere with electrically charged black hole and spatially distributed external electric charge. Thus, charging of black holes does not invalidate the Blandford-Znajek mechanism.
S. Komissarov
Thu, 19 Aug 21
29/54
Comments: to be submitted to MNRAS, comments welcome