Supermassive black hole formation in the initial collapse of axion dark matter

Abstract

Axion dark matter thermalizes by gravitational self-interactions and forms a Bose-Einstein condensate. We show that the rethermalization of the axion fluid during the initial collapse of large scale overdensities near cosmic dawn transports angular momentum outward sufficientlly fast that black holes form with masses ranging from approximately $10^5$ to a few times $10^{10}~M_\odot$. This conclusion holds for QCD axions and for axion-like particles of mass larger than $10^{-16}$ eV/$c^2$.