Black holes and gravitational waves in models of minicharged dark matter

TL;DR

This paper explores how gravitational-wave observations can constrain the charge of black holes in models of minicharged dark matter, revealing potential electromagnetic signals and new bounds on dark sector properties.

Contribution

It introduces observational bounds on black hole charge from gravitational waves and analyzes the excitation of dark photon modes during mergers in minicharged dark matter models.

Findings

Gravitational-wave data constrains black hole charge in dark matter models.

Dark photon bursts may accompany black hole mergers.

Near-extremal black holes strongly excite dark electromagnetic modes.

Abstract

In viable models of minicharged dark matter, astrophysical black holes might be charged under a hidden $U(1)$ symmetry and are formally described by the same Kerr-Newman solution of Einstein-Maxwell theory. These objects are unique probes of minicharged dark matter and dark photons. We show that the recent gravitational-wave detection of a binary black-hole coalescence by aLIGO provides various observational bounds on the black hole's charge, regardless of its nature. The pre-merger inspiral phase can be used to constrain the dipolar emission of (ordinary and dark) photons, whereas the detection of the quasinormal modes set an upper limit on the final black hole's charge. By using a toy model of a point charge plunging into a Reissner-Nordstrom black hole, we also show that in dynamical processes the (hidden) electromagnetic quasinormal modes of the final object are excited to considerable amplitude in the gravitational-wave spectrum only when the black hole is nearly extremal. The coalescence produces a burst of low-frequency dark photons which might provide a possible electromagnetic counterpart to black-hole mergers in these scenarios.