  We analyze the observed distribution of Eddington ratios as a function of
supermassive black hole mass for a large sample of nearby galaxies drawn from
the Sloan Digital Sky Survey. We demonstrate that there are two distinct
regimes of black hole growth in nearby galaxies. The first is associated with
galaxies with significant star formation in their central kiloparsec regions,
and is characterized by a broad log-normal distribution of accretion rates
peaked at about one percent of the Eddington limit. In this regime, the
Eddington ratio distribution is independent of the mass of the black hole and
shows no further dependence on the central stellar population of the galaxy.
The second regime is associated with galaxies with old central stellar
populations, and is characterized by a power-law distribution function of
Eddington ratios. In this regime, the time-averaged mass accretion rate onto
black holes is proportional to the mass of stars in the galaxy bulge, with a
constant of proportionality that depends on the mean stellar age of the stars.
This result is once again independent of black hole mass. We show that both the
slope of the power-law and the decrease in the accretion rate onto black holes
in old galaxies are consistent with population synthesis model predictions of
the decline in stellar mass loss rates as a function of mean stellar age. Our
results lead to a very simple picture of black hole growth in the local
Universe. If the supply of cold gas in a galaxy bulge is plentiful, the black
hole regulates its own growth at a rate that does not further depend on the
properties of the interstellar medium. Once the gas runs out, black hole growth
is regulated by the rate at which evolved stars lose their mass.
