Dark magnetohydrodynamics: Black hole accretion in superradiant dark photon clouds

TL;DR

This paper explores how a superradiant dark photon cloud around a black hole interacts with accretion flows, revealing potential modifications like increased wind launching and oscillations depending on the coupling strength.

Contribution

It extends general-relativistic magnetohydrodynamics to include dark photon effects and numerically investigates their impact on black hole accretion flows.

Findings

Dark photon coupling can enhance wind launching from accretion disks.

Oscillation modes in the disk are influenced by the dark photon interaction.

The study provides a first numerical analysis of dark photon effects on accretion dynamics.

Abstract

Black holes threaded by massive vector fields can be subject to a superradiant instability, growing a cloud of massive vector particles around it. In this work, we consider what happens if such a dark matter candidate field mimicking a dark photon interacts with an accretion flow onto the black hole. By including a kinetic mixing term with the standard model photon, we extend the commonly used equations of general-relativistic magnetohydrodynamics to a dark photon constituent. The coupling to the dark photon then appears as an effective dynamo term together with a dark Lorentz force acting on the accreting matter. We numerically study the interactions between the superradiant dark photon cloud and the inner accretion flow by solving the coupled system in full numerical relativity. By parameterically varying the mixing parameter between dark and standard model sector, we provide a first investigation of how the accretion flow could be modified. Depending on the coupling strength, our solutions exhibit increased wind launching, as well as oscillation modes in the disk.