Star Formation in Accretion Disks and SMBH Growth
  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.
