Collisions of charged black holes

TL;DR

This paper presents detailed numerical simulations of head-on collisions of charged black holes, analyzing gravitational and electromagnetic radiation, and compares results with analytic models, revealing how charge influences collision dynamics and emitted radiation.

Contribution

First fully non-linear simulations of charged black hole collisions that compare numerical results with analytic expectations, highlighting charge effects on radiation and dynamics.

Findings

Electromagnetic to gravitational radiation ratio reaches 22% at high charge.

Gravitational wave energy decreases significantly with increasing charge.

Ringdown frequencies match perturbative predictions.

Abstract

We perform fully non-linear numerical simulations of charged-black-hole collisions, described by the Einstein-Maxwell equations, and contrast the results against analytic expectations. We focus on head-on collisions of non-spinning black holes, starting from rest and with the same charge to mass ratio, Q/M. The addition of charge to black holes introduces a new interesting channel of radiation and dynamics, most of which seem to be captured by Newtonian dynamics and flat-space intuition. The waveforms can be qualitatively described in terms of three stages; (i) an infall phase prior to the formation of a common apparent horizon; (ii) a nonlinear merger phase which corresponds to a peak in gravitational and electromagnetic energy; (iii) the ringdown marked by an oscillatory pattern with exponentially decaying amplitude and characteristic frequencies that are in good agreement with perturbative predictions. We observe that the amount of gravitational-wave energy generated throughout the collision decreases by about three orders of magnitude as the charge-to-mass ratio Q/M is increased from 0 to 0.98. We interpret this decrease as a consequence of the smaller accelerations present for larger values of the charge. In contrast, the ratio of energy carried by electromagnetic to gravitational radiation increases, reaching about 22% for the maximum Q/M ratio explored, which is in good agreement with analytic predictions.