Dark photon superradiance: Electrodynamics and multimessenger signals

TL;DR

This paper explores the electrodynamics of dark photon clouds around spinning black holes, predicting observable multimessenger signals like X-ray emissions and gravitational waves, and proposes strategies for their detection.

Contribution

It introduces a novel model of dark photon superradiance clouds, analyzing their electrodynamics and emission signatures using magnetohydrodynamics techniques, and suggests observational methods for detection.

Findings

Peak luminosity up to 10^43 erg/s for solar-mass black holes

Emission likely includes significant X-ray components

Potential periodic signals related to dark photon mass

Abstract

We study the electrodynamics of a kinetically mixed dark photon cloud that forms through superradiance around a spinning black hole, and design strategies to search for the resulting multimessenger signals. A dark photon superradiance cloud sources a rotating dark electromagnetic field which, through kinetic mixing, induces a rotating visible electromagnetic field. Standard model charged particles entering this field initiate a transient phase of particle production that populates a plasma inside the cloud and leads to a system which shares qualitative features with a pulsar magnetosphere. We study the electrodynamics of the dark photon cloud with resistive magnetohydrodynamics methods applicable to highly magnetized plasma, adapting techniques from simulations of pulsar magnetospheres. We identify turbulent magnetic field reconnection as the main source of dissipation and electromagnetic emission, and compute the peak luminosity from clouds around solar-mass black holes to be as large as $10^{43}$ erg/s for open dark photon parameter space. The emission is expected to have a significant X-ray component and is potentially periodic, with period set by the dark photon mass. The luminosity is comparable to the brightest X-ray sources in the Universe, allowing for searches at distances of up to hundreds of Mpc with existing telescopes. We discuss observational strategies, including targeted electromagnetic follow-ups of solar-mass black hole mergers and targeted continuous gravitational wave searches of anomalous pulsars.