Some results on the evolution of primordial black holes

Abstract

We briefly review some recent results related to thermodynamics of semiclassical black holes applied to their primordial formation. Issues on the existence of an influx of ambient particles onto the PBHs, which may help grow them, are addressed. We revisit the integrated flux from evaporated PBHs contributing to the present backgrounds and show that there probe mass scales which are otherwise poorly constrained. Finally the Generalized Second Law of Thermodynamics and the Holographic Principle are combined to show that if some form of the latter holds, strong upper bounds to the mass density of PBHs formed in the early universe may be obtained, especially for inflationary cosmological models. This method is completely independent from those based on the background fluxes and applies to potentially important epochs of PBH formation, resulting in quite strong constraints to Ω pbh .

Ultrarelativistic Bondi–Hoyle accretion – I. Axisymmetry

“…Some authors show that the calculated accretion rates for simplified models are sufficiently high to transform a PBH to solar mass black holes (Sivaram 2001). As cited above, others make claims that when more complicated accretion models are considered, the mass accretion rates for both stationary and moving PBHs are insufficient to appreciably modify the mass of the PBH except in very high Lorentz factor models (Custodio and Horvath 2002;Horvath and Custodio 2005). We show, using our own simplified model, that the accretion rates of moving PBH is insufficient for the PBH to reach solar masses, in agreement with the conclusions of Custodio and Horvath (2002).…”

“…By comparing our accretion rates to that of the results in Horvath and Custodio (2005), we also find that our models of traveling black holes do not substantially increase their mass accretion rate. This leads us to agree with the conclusions of Custodio and Horvath (2002) and Horvath and Custodio (2005), that a primordial black hole must sustain a very large boost to begin to accrete sufficient amounts of matter to completely avoid Hawking radiation. When comparing fluid models for Γ = 1.1, 5/4, 4/3, and 3/2 in figures B1, 7, B3, and B2, we find that the stiffer the fluid Γ → 2, the faster the accretion rate.…”

Feasibility of primordial black hole Remnants as dark matter in view of Hawking radiation recoil

“…In the non-commutative case discussed here, however, the maximum temperature occurs way before Planck temperature, and so the speed is negligible for most part of the evolution before M m is reached. Now, according to [54] and [64], if the Hawking temperature of a black hole reaches T ≈ 2.7 K at the current epoch, it will attain thermal equilibrium with the cosmic microwave background (CMB) photons and thus stop evaporating. While this may be true for larger black holes, it is not what happens in our case when the black holes are microscopic.…”