Black holes as particle detectors: evolution of superradiant instabilities

TL;DR

This study investigates the nonlinear evolution of superradiant instabilities in spinning black holes, showing that gravitational waves are negligible but accretion significantly influences the process, supporting the validity of linear models.

Contribution

First comprehensive analysis of gravitational-wave emission and gas accretion effects on superradiant instabilities in black holes, validating linear approximations.

Findings

Gravitational-wave emission has minimal impact on black hole evolution.

Gas accretion significantly affects the development of superradiant clouds.

Backreaction of the scalar cloud is negligible despite large mass fractions.

Abstract

Superradiant instabilities of spinning black holes can be used to impose strong constraints on ultralight bosons, thus turning black holes into effective particle detectors. However, very little is known about the development of the instability and whether its nonlinear time evolution accords to the linear intuition. For the first time, we attack this problem by studying the impact of gravitational-wave emission and gas accretion on the evolution of the instability. Our quasi-adiabatic, fully-relativistic analysis shows that: (i) gravitational-wave emission does not have a significant effect on the evolution of the black hole, (ii) accretion plays an important role and (iii) although the mass of the scalar cloud developed through superradiance can be a sizeable fraction of the black-hole mass, its energy-density is very low and backreaction is negligible. Thus, massive black holes are well described by the Kerr geometry even if they develop bosonic clouds through superradiance. Using Monte Carlo methods and very conservative assumptions, we provide strong support to the validity of the linearized analysis and to the bounds of previous studies.