Black hole foraging: feedback drives feeding
  We suggest a new picture of supermassive black hole (SMBH) growth in galaxy
centers. Momentum-driven feedback from an accreting hole gives significant
orbital energy but little angular momentum to the surrounding gas. Once central
accretion drops, the feedback weakens and swept-up gas falls back towards the
SMBH on near-parabolic orbits. These intersect near the black hole with
partially opposed specific angular momenta, causing further infall and
ultimately the formation of a small-scale accretion disk. The feeding rates
into the disk typically exceed Eddington by factors of a few, growing the hole
on the Salpeter timescale and stimulating further feedback. Natural
consequences of this picture include (i) the formation and maintenance of a
roughly toroidal distribution of obscuring matter near the hole; (ii) random
orientations of successive accretion disk episodes; (iii) the possibility of
rapid SMBH growth; (iv) tidal disruption of stars and close binaries formed
from infalling gas, resulting in visible flares and ejection of hypervelocity
stars; (v) super-solar abundances of the matter accreting on to the SMBH; and
(vi) a lower central dark-matter density, and hence annihilation signal, than
adiabatic SMBH growth implies. We also suggest a simple sub-grid recipe for
implementing this process in numerical simulations.
