Survival of the Fittest: Testing Superradiance Termination with Simulated Binary Black Hole Statistics

TL;DR

This paper investigates how tidal interactions in black hole binaries affect superradiant boson clouds, revealing that certain modes are more resilient and that surviving clouds are more detectable, based on large-scale simulated data.

Contribution

First analysis of superradiance termination effects on black hole binaries using realistic Galactic population simulations, identifying conditions for cloud survival.

Findings

$l=m=1$ modes are generally stable against termination

$l=m=2$ modes have survival rates below 10% for certain boson masses

Surviving clouds tend to have higher growth rates and detection prospects

Abstract

The superradiance instability of rotating black holes leads to the formation of an ultralight boson cloud with distinctive observational signatures, making black holes an effective probe of ultralight bosons. However, around black holes in a binary system, the superradiance effect of such clouds can be terminated by tidal perturbations from the companion, leading to cloud depletion. In this study, we focus on the superradiance of a scalar boson, and perform the first analysis of the impact of this termination effect on superradiant black hole binaries which are realistically modeled after their statistics in our Galaxy. Working with a dataset of approximately $10^7$ black hole binaries simulated using the Stellar EVolution for N-body (SEVN) population synthesis code, we identify the superradiant candidates and those that manage to survive the termination effect. We then calculate the cloud survival rate for various boson masses and black hole spin models. Our findings reveal that the $l=m=1$ cloud modes are generally stable against termination, whereas the $l=m=2$ modes can be significantly affected, with survival rates dropping below $10\%$ for boson masses below approximately $0.5\times 10^{-12}$ eV. In addition, our analysis indicates that clouds that overcome termination typically exhibit a higher superradiant growth rate and therefore a higher detectability.