Clusters of primordial black holes

TL;DR

This paper explores the formation and evolution of primordial black hole clusters, proposing they could explain various cosmic phenomena and serve as dark matter candidates, while potentially bypassing existing constraints on single PBHs.

Contribution

It introduces a novel model of PBH clusters formed through inflationary processes and particle decay, offering advantages over single PBH models in explaining observations.

Findings

PBH clusters can form via inflationary domain walls and particle decay.

Clusters may explain supermassive black holes and gravitational wave events.

Clusters could serve as dark matter candidates and account for gamma-ray sources.

Abstract

The Primordial Black Holes (PBHs) are gradually involved into consideration as the phenomenon having reliable basis. We discuss here the possibility of their agglomeration into clusters that may have several prominent observable features. The clusters can form due to closed domain walls appearance in the natural and the hybrid inflation with subsequent evolution and gravitational collapse. Early dustlike stages of dominance of heavy metastable dissipative particles, at which star-like objects are formed, can also naturally lead to formation of black hole clusters, remaining in the Universe after decay of particles, from which they have originated. The dynamical evolution of such clusters discussed here is of the crucial importance. Such a model inherits all the advantages of the single PBHs like possible explanation of existence of supermassive black holes (origin of the early quasars), binary BH merges registered by LIGO/Virgo through gravitational waves, contribution to reionization of the Universe, but also has additional benefits. The cluster could alleviate or completely avoid existing constraints on the single PBH abundance making PBHs a real dark matter candidate. The most of existing constraints on (single) PBH density should be re-considered as applied to the clusters. Also unidentified cosmic gamma-ray point-like sources could be (partially) accounted for by them. One can conclude, that it seems really to be much more viable model with respect to the single PBHs.