Bosenova collapse of axion cloud around a rotating black hole

TL;DR

This paper investigates the nonlinear dynamics of axion clouds around rotating black holes, revealing a collapse phenomenon called bosenova, driven by superradiant instability and nonlinear self-interactions, supported by numerical simulations and theoretical analysis.

Contribution

It provides the first numerical evidence of bosenova collapse of axion clouds around black holes and develops an effective wavepacket theory to explain this phenomenon.

Findings

Axion clouds undergo collapse due to nonlinear effects.

Bosenova occurs when the axion field reaches a critical amplitude.

Theoretical model explains the onset of collapse.

Abstract

Motivated by possible existence of stringy axions with ultralight mass, we study the behavior of an axion field around a rapidly rotating black hole (BH) obeying the sine-Gordon equation by numerical simulations. Due to superradiant instability, the axion field extracts the rotational energy of the BH and the nonlinear self-interaction becomes important as the field grows larger. We present clear numerical evidences that the nonlinear effect leads to a collapse of the axion cloud and a subsequent explosive phenomena, which is analogous to the "bosenova" observed in experiments of Bose-Einstein condensate. The criterion for the onset of the bosenova collapse is given. We also discuss the reason why the bosenova happens by constructing an effective theory of a wavepacket model under the nonrelativistic approximation.