Gravitational wave signatures of ultralight vector bosons from black hole superradiance

TL;DR

This paper models gravitational wave signals from ultralight vector bosons around black holes, providing detailed predictions across parameter spaces and identifying unique signals from mode beating, aiding dark matter detection efforts.

Contribution

It offers relativistically accurate gravitational wave predictions for ultralight vector bosons, filling gaps between previous approximations and calculations, and explores mode interactions in superradiance.

Findings

Relativistic corrections significantly affect gravitational wave amplitude estimates.

Overtone modes can grow faster than fundamental modes, producing distinct signals.

The study maps out parameter spaces where different superradiant modes dominate.

Abstract

In the presence of an ultralight bosonic field, spinning black holes are unstable to superradiance. The rotational energy of the black hole is converted into a non-axisymmetric, oscillating boson cloud which dissipates through the emission of nearly monochromatic gravitational radiation. Thus, gravitational wave observations by ground- or space-based detectors can be used to probe the existence of dark particles weakly coupled to the Standard Model. In this work, we focus on massive vector bosons, which grow much faster through superradiance, and produce significantly stronger gravitational waves compared to the scalar case. We use techniques from black hole perturbation theory to compute the relativistically-correct gravitational wave signal across the parameter space of different boson masses and black hole masses and spins. This fills in a gap in the literature between flatspace approximations, which underestimate the gravitational wave amplitude in the non-relativistic limit, and overestimate it in the relativistic regime, and time-domain calculations, which have only covered a limited part of the parameter space. We also identify parameter ranges where overtone superradiantly unstable modes will grow faster than the lower frequency fundamental modes. Such cases will produce a distinct gravitational wave signal due to the beating of the simultaneously populated modes, which we compute.