# Follow-up signals from superradiant instabilities of black hole merger remnants

## TL;DR

This paper explores how gravitational wave signals from bosonic clouds around black hole merger remnants can reveal ultralight bosons, analyzing detection prospects with future detectors and the impact of background noise.

## Contribution

It provides a detailed analysis of the parameter space for detecting post-merger signals from ultralight scalar clouds using future gravitational wave detectors.

## Key findings

- Cosmic Explorer could detect dozens of post-merger signals under optimistic assumptions.
- Detection prospects depend on the astrophysical priors and noise conditions.
- Confusion noise from stochastic backgrounds can affect the sensitivity of searches.

## Abstract

Superradiant instabilities can trigger the formation of bosonic clouds around rotating black holes. If the bosonic field growth is sufficiently fast, these clouds could form shortly after a binary black hole merger. Such clouds are continuous sources of gravitational waves whose detection (or lack thereof) can probe the existence of ultralight bosons (such as axion-like particles) and their properties. Motivated by the binary black hole mergers seen by Advanced LIGO so far, we investigate in detail the parameter space that can be probed with continuous gravitational wave signals from ultralight scalar field clouds around black hole merger remnants with particular focus on future ground-based detectors (A+, Voyager and Cosmic Explorer). We also study the impact that the confusion noise from a putative stochastic gravitational-wave background from unresolved sources would have on such searches and we estimate, under different astrophysical priors, the number of binary black-hole merger events that could lead to an observable post-merger signal. Under our most optimistic assumptions, Cosmic Explorer could detect dozens of post-merger signals.