Salpeter timescale

The Salpeter timescale (or Salpeter time) is a timescale for a limit on black hole growth, specifically presuming accretion does not exceed the Eddington limit. A growing black hole heats the material it is accreting to the point that it glows, and at some level of accretion, the resulting luminosity's radiation pressure would presumably fully counteract the accretion, resulting in a limit on the possible accretion rate. The timescale is roughly 5×10⁷ years, which suggests a black hole will grow to no more than a factor of e in that many years (i.e., an e-folding time). Of interest is that though this timescale allows plenty of time for the growth of today's most massive supermassive black holes (SMBHs), it leaves insufficient time for such growth of the substantial SMBHs presumed to power observed distant quasars. This implies some black hole formation or growth mechanism not limited by Eddington luminosity (or some more-radical adjustment to cosmological models).