A tepid model for the early universe

If the Universe started off with a photon-to-baryon ratio much less than presently observed, massive black holes would have formed at early times even if the initial density fluctuations were very small. These holes could have generated the rest of the background radiation through accretion; in this way, such a Universe might automatically evolve to have the photon-to-baryon ratio observed today. This scenario could explain why the times of decoupling and matterradiation equilibrium are comparable and might provide a critical density of primordial black holes; it could also produce galaxies with black hole 'halos'. If the initial photon-to-baryon ratio was large enough, black hole formation would not occur: one would then have to invoke an alternative scenario in which the rest of the background radiation was generated by primordial stars at a comparatively recent epoch. (orig.)