CMB and accretion

TL;DR

This paper reviews how primordial black holes could influence the early universe's ionization and CMB anisotropies through accretion, highlighting current constraints on their abundance and properties.

Contribution

It provides a comprehensive review of the effects of PBH accretion on the cosmological medium and summarizes existing observational constraints.

Findings

Accretion onto PBHs can significantly alter the ionization history.

CMB anisotropies are sensitive probes of PBH properties.

Current constraints limit the abundance of certain PBH mass ranges.

Abstract

Primordial black holes (PBHs) of stellar mass or heavier would accrete baryonic gas, which becomes denser and hotter, injecting energetic photons in the cosmological medium soon after cosmic recombination, in the so-called dark ages. The ionisation history of the universe would be altered, an effect cosmic microwave background (CMB) temperature and polarisation anisotropies is sensitive to. The magnitude of the effect depends on the abundance and mass distribution of the PBHs, as well as on still uncertain aspects of accretion luminosity. We review the current understanding of this field, with an emphasis on the peculiarities of the phenomenon in the cosmological context, and present the existing constraints on the PBH abundances.