Gravitational superfluorescence from superradiant axion clouds

Abstract

Boson clouds formed via superradiance around spinning black holes offer a novel probe of ultralight particles. We show that such gravitational atoms can undergo a self-stimulated avalanche: a coherent quadrupolar transition is seeded by external gravitational waves and amplified by self-generated radiation feedback. We formulate an effective two-level description, validated by numerical simulations, that captures the logistic population transfer and the resulting delayed gravitational-wave pulse with a characteristic envelope, and assess its detectability with future detectors. As a gravitational analogue of superfluorescence, this cooperative emission mechanism opens a new observational avenue into the ultralight dark sector.

v1: 7 pages, 2 figures, 2 tables; Supplemental Material with 1 figure and 1 table; v2: minor corrections; clarified the ignition-delay discussion; conclusions unchanged