Axion clouds may survive the perturbative tidal interaction over the early inspiral phase of black hole binaries

TL;DR

This paper investigates how axion clouds around rotating black holes interact with binary systems, revealing conditions under which these clouds can survive tidal interactions during inspiral phases.

Contribution

The study provides a comprehensive numerical analysis of axion cloud depletion in binary black hole systems, focusing on the effects of quadrupolar tidal perturbations across various parameters.

Findings

Cloud survival occurs only for the l=1 mode as the fastest growing mode.

Counter-rotating binary orbits help preserve the axion cloud.

Tidal effects can deplete the cloud unless specific conditions are met.

Abstract

Gravitational wave observation has the potential of probing ultralight bosonic fields such as axion. Axion forms a cloud around a rotating black hole (BH) by superradiant instability and should affect the gravitational waveform from binary BHs. On the other hand, considering the cloud associated with a BH in a binary system, tidal interaction depletes the cloud in some cases during the inspiral phase. We made the exhaustive study of cloud depletion numerically in a wide parameter range for equal mass binaries, assuming only the quadrupolar tidal perturbation is at work. We found that clouds can avoid disappearing due to the tidal effect only when $l=1$ mode is the fastest growing mode and when the binary orbit is counter-rotating in the non-relativistic parameter region.