Electromagnetic emission from axionic clouds and the quenching of superradiant instabilities

TL;DR

This paper demonstrates that dense axionic clouds around spinning black holes can produce laser-like electromagnetic emission through classical processes, providing a new understanding of superradiant instabilities and their observational signatures.

Contribution

The study offers the first quantitative classical analysis of electromagnetic emission from axionic clouds, revealing laser-like phenomena induced by axion-photon couplings.

Findings

Laser-like emission from axionic clouds exists at the classical level.

Numerical solutions confirm the occurrence of stimulated emission.

Provides a quantitative description of electromagnetic emission mechanisms.

Abstract

The nature of dark matter is one of the longest-standing puzzles in science. Axions or axion-like particles are a key possibility, and arise in mechanisms to solve the strong CP problem but also in low-energy limits of string theory. Extensive experimental and observational efforts are actively looking for `axionic' imprints. Independently on their nature, their abundance, and on their contribution to the dark matter problem, axions form dense clouds around spinning black holes, grown by superradiant mechanisms. It was recently suggested that once couplings to photons are considered, an exponential (quantum) stimulated emission of photons ensues at large enough axion number. Here we solve numerically the classical problem in different setups. We show that laser-like emission from clouds exists at the classical level, and we provide the first quantitative description of the problem.