Star Formation in Accretion Disks and SMBH Growth

TL;DR

This paper investigates how star formation in accretion disks around supermassive black holes can significantly accelerate black hole growth by providing additional mass through compact objects, potentially explaining rapid black hole formation.

Contribution

It introduces models showing that star formation and compact object infall can greatly increase SMBH growth rates without requiring super-Eddington gas accretion.

Findings

Black hole growth timescales can decrease by up to 90%.

Star formation in accretion disks can lead to rapid SMBH mass doubling.

Implications for high-redshift massive black hole formation.

Abstract

Accretion disks around active galactic nuclei are potentially unstable to star formation at large radii. We note that when the compact objects formed from some of these stars spiral into the central supermassive black hole, there is no radiative feedback and therefore the accretion rate is not limited by radiation forces. Using a set of accretion disk models, we calculate the accretion rate onto the central supermassive black hole in both gas and compact objects. We find that the timescale for a supermassive black hole to double in mass can decrease by factors ranging from $\sim0.7$ to as low as $\sim0.1$ in extreme cases, compared to gas accretion alone. Our results suggest that the formation of extremely massive black holes at high redshift may occur without prolonged super-Eddington gas accretion or very massive seed black holes. We comment on potential observational signatures as well as implications for other observations of active galactic nuclei.