  It has long been recognised that the main obstacle to accretion of gas onto
supermassive black holes (SMBHs) is large specific angular momentum. It is
feared that the gas settles in a large scale disc, and that accretion would
then proceed too inefficiently to explain the masses of the observed SMBHs.
Here we point out that, while the mean angular momentum in the bulge is very
likely to be large, the deviations from the mean can also be significant.
Indeed, cosmological simulations show that velocity and angular momentum fields
of gas flows onto galaxies are very complex. Furthermore, inside bulges the gas
velocity distribution can be further randomised by the velocity kicks due to
feedback from star formation. We perform hydrodynamical simulations of gaseous
rotating shells infalling onto an SMBH, attempting to quantify the importance
of velocity dispersion in the gas at relatively large distances from the black
hole. We implement this dispersion by means of a supersonic turbulent velocity
spectrum. We find that, while in the purely rotating case the circularisation
process leads to efficient mixing of gas with different angular momentum,
resulting in a low accretion rate, the inclusion of turbulence increases this
accretion rate by up to several orders of magnitude. We show that this can be
understood based on the notion of "ballistic" accretion, whereby dense
filaments, created by convergent turbulent flows, travel through the ambient
gas largely unaffected by hydrodynamical drag. We derive a simple analytical
formula that captures the numerical results to within a factor of a few.
Rescaling our results to astrophysical bulges, we argue that this "ballistic"
mode of accretion could provide the SMBHs with a sufficient supply of fuel
without the need to channel the gas via large-scale discs or bars, and
therefore that star formation in bulges can be a strong catalyst for SMBH
accretion.
