REIONIZATION OF THE UNIVERSE BY EARLY-FORMED MASSIVE BLACK-HOLES

Based on a recently proposed scenario for the early formation of massi ve black holes, the possibility that the universe is reionized as a re sult of the UV radiation from such black holes is investigated. A two- step scenario for the formation of an active compact nucleus is consid ered: First, an angular momentum-supported disk shrinks into a compact disk because of the Compton drag with the cosmic background radiation (CBR). Second, the disk is adiabatically heated, and then turbulent v iscosity works to convert the gravitational energy into powerful radia tion. Within this context, it is found that the overall reionization o f the universe by high-redshift black hole systems is possible. The re ionization epoch depends upon the power-law index of the density fluct uations at the recombination epoch. If the spectral index is in the ra nge of n greater than or similar to -1.7, the universe is reionized ov erall by z similar to 150, having a Gunn-Peterson optical depth below the 2 sigma upper limits inferred from recent observations of QSOs at 2.6 < z < 4.2. The UV flux from early-formed massive black holes may p rovide additional sources of UV background intensity to satisfy the '' proximity effect'' of Ly alpha absorption lines in QSO spectra. In add ition, the Compton y-parameter of the CBR is considerably below the ob served upper limits from COBE results. If n less than or similar to -1 .5, the results are not in conflict with the observed soft X-ray backg round. The predicted helium Gunn-Peterson effect and mass function of relic black holes are also presented.