Near-horizon microstructure and superradiant instability of black holes

TL;DR

This paper investigates how the microstructure near a black hole's horizon affects superradiant instability and the evolution of boson clouds, with implications for gravitational wave detection of ultralight bosons.

Contribution

It introduces a reflection parameter to model near-horizon microstructure and derives analytical corrections to superradiance characteristics.

Findings

Near-horizon microstructure influences superradiant instability.

Analytical corrections to energy levels and frequencies derived.

Implications for gravitational wave signals from boson clouds.

Abstract

Ultralight bosons, as important candidates of dark matter, can condense around spinning black holes (BHs) to form long-lived ``boson clouds'' due to superradiance instability. The boson-BH system can be observed through gravitational wave detection and may become a new window to find traces of ultralight bosons. In this letter we explore the effects on the superradiant instability of BHs from the near-horizon microstructure. By introducing the reflection parameter near a BH horizon, we derived analytical results on the corrections to both energy levels of bosonic cloud and its characteristic frequencies of superradiance instability. Our results imply that the evolution of a boson-BH system and gravitational waves it emits would be influenced by the near-horizon physics of a BH.