MASSIVE BLACK-HOLES AND LIGHT-ELEMENT NUCLEOSYNTHESIS IN A BARYONIC UNIVERSE

We reexamine the model proposed by Gnedin & Ostriker (1992) in which Jeans mass black holes (M(BH) almost-equal-to 10(6) M.) form shortly after decoupling. There is no nonbaryonic dark matter in this model, but we examine the possibility that OMEGA(b) is considerably larger than given by normal nucleosynthesis. Here we allow for the fact that much of the high baryon-to-photon ratio material will collapse leaving the universe of remaining material with light-element abundances more in accord with the residual baryonic density (approximately 10(-2)) than with OMEGA0 and the initial baryonic density (approximately 10(-1)). We find that no reasonable model can be made with random-phase density fluctuations, if the power on scales smaller than 10(6) M. is as large as expected. However, phase-correlated models of the type that might occur in connection with topological singularities can be made with OMEGA(b)h2 = 0.013 +/- 0.001, 0.15 less-than-or-similar-to OMEGA0 less-than-or-similar-to 0.4, which are either flat (OMEGA(LAMBDA) = 1 - OMEGA0) or open (OMEGA(LAMBDA) = 0) and which satisfy all the observational constraints which we apply, including the large baryon-to-total mass ratio found in the X-ray clusters. The remnant baryon density is thus close to that obtained in the standard picture (OMEGA(b)h2 = 0.0125 +/- 0.0025; Walker et al. 1998). The spectral index implied for fluctuations in the baryonic isocurvature scenario, - 1 < m < 0, is in the range expected by other arguments based on large-scale structure and microwave fluctuation constraints. The dark matter in this picture is in the form of massive black holes. Accretion onto them at early epochs releases high-energy photons which significantly heat and reionize the universe. But photodissociation does not materially change light-element abundances. A typical model gives yBAR almost-equal-to 1 x 10(-5), n(e)/n(H)(z = 30) almost-equal-to 0.1, and a diffuse gamma-ray background at 100 keV near the COBE limit of the order of 10% of that observed which originates from high-redshift quasars. Reionization in this model occurs at redshift 600 and reaches (H II/H(tot)) almost-equal-to 0.1-0.2.