The Gunn Peterson Effect: a Test for a Black Holes Induced Photoionization of the Intergalactic Medium
- Marina Gibilisco
In this paper I will discuss the possibility of a reionization of the Universe due to the photons emitted by evaporating primordial black holes (PBHs); this process should happen during the last stages of the PBHs life, when the particle emission is very intense. I will study the time evolution of the ionization degree x, of the plasma temperature Te and of the photon number density nγ characterizing the Universe after the recombination epoch: a system of coupled differential equations for these variables is solved in an analytical way, by assuming, as a photon source, PBHs having an initial mass M ∼ 10 g. I will also take into account the PBH emission of quarks and gluons jets, which should be expected from PBHs having a temperature T > ΛQCD. The results I obtain prove that such a kind of reionization is possible, being able to increase the ionization degree of the Universe from a value x = 0.002 (just after the recombination) to values near 1 (when the black holes evaporation ends); in the same time, the rise of the plasma temperature Te is limited by powerful cooling effects; therefore, such a reionization model does not predict an excessive distortion of the Cosmic Microwave Background (CMB) spectrum, in agreement with the experimental FIRAS data on the comptonization parameter yc (yc < 2.5× 10 ). 1. PBH QUANTUM EVAPORATION AND PHOTON EMISSION SPECTRUM. The possibility that the Universe was reionized after the recombination is strongly suggested by many experimental evidences as, for instance, the Gunn Peterson test . The causes of such a reionization for the Universe are unclear and, in general, a complete theory describing this phenomenon is not yet available.