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

Abstract

Abstract The superradiance instability of rotating black holes (BHs) leads to the formation of an ultralight boson cloud with distinctive observational signatures, making BHs an effective probe of ultralight bosons. However, around BHs 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 BH binaries, which are realistically modeled after their statistics in our Galaxy. Working with a data set of approximately 107 BH binaries simulated using the Stellar Evolution for N-body 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 BH 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 × 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.