Pregalactic black hole accretion and the thermal history of the Universe

Pregalactic black holes could have a large luminosity at early times due to accretion. Holes with mass exceeding about 103 ∈−1 M (where ∈ is the radiative ‘efficiency’ factor) would necessarily radiate at the Eddington limit for some period after decoupling, and large enough holes might do so until galaxy formation. The consequent radiation production could have an important effect on the thermal history of the Universe, even if the density of the holes is small. In general the matter temperature would be boosted well above its Friedmann value and, for a wide range ot values for the mass and density of the holes, the matter would be completely re-ionized. In some circumstances, the Universe would never pass through a neutral phase at all. Black hole accretion before decoupling may conceivably have generated the 3 K background radiation, but only if the holes’ luminosity exceeded the Eddington limit.