Charging up boosted black holes

Abstract

Contrary to a prevailing assumption that black holes would swiftly discharge, we argue that black holes can charge preferentially when boosted through an ambient magnetic field. Though the details are very different, the preference for charge is related to the precipitation of the Wald charge on a spinning black hole in an ambient magnetic field. The gravito-electrodynamics upstage naive arguments about screening electric fields-in vacuum-in determining the value of the charge accrued. Charged test particles, which build up the black hole charge, exhibit chaotic behavior as evidenced by fractal basin boundaries between dynamical regions. Charged, boosted black holes will generate their own electromagnetic fields and thereby their own luminous signatures, even if they are initially bare. We therefore add boosted black holes to the growing list of potentially observable black hole signatures, alongside black hole batteries and black hole pulsars. The implications should be relevant for supermassive black holes that are boosted relative to a galactic magnetic field as well as black holes merging with magnetized neutron stars.

Magnetized Black Holes: Interplay between Charge and Rotation

“…Let us note that the mechanism of charging of a boosted black hole in translatory motion has been revisited very recently, [44,45]; it has attracted renewed widespread attention because of its tentative relevance for late stages of black hole-neutron star inspirals and their subsequent mergers. In this context, there is an interesting parallel between the effects of rotation vs. boost.…”

Spinning black holes with axion hair

“…A particular instance is found in self-interacting dark matter models, featuring a dark photon uncoupled to Standard Model particles [43][44][45][46]. Additionally, galactic magnetic fields could charge moving black holes [47]. These models hint at the possibility of astrophysical black holes featuring notably high charge-to-mass ratios, further adding to the motivation of studying black holes featuring an axionic-type coupling.…”