Abstract
We explore the possibility that Dark Matter (DM) may be explained by a nonuniform background of approximately stellar mass clusters of Primordial Black Holes (PBHs) by simulating the evolution from recombination to the present with over 5000 realisations using a Newtonian N-body code. We compute the cluster rate of evaporation and extract the binary and merged sub-populations along with their parent and merger tree histories, lifetimes and formation rates, the dynamical and orbital parameter profiles, the degree of mass segregation and dynamical friction and power spectrum of close encounters. Overall, we find that PBHs can constitute a viable DM candidate, and that their clustering presents a rich phenomenology throughout the history of the Universe. We show that binary systems constitute about 9.5% of all PBHs at present, with mass ratios of q¯B=0.154, and total masses of m¯T,B=303M⊙. Merged PBHs are rare, about 0.0023% of all PBHs at present, with mass ratios of q¯B=0.965 with total and chirp masses of m¯T,B=1670M⊙ and m¯c,M=642M⊙, respectively. We find that cluster puffing up and evaporation leads to bubbles of these PBHs of order 1 kpc containing at present times about 36% of objects and mass, with one-hundred pc-sized cores. We also find that these PBH sub-haloes are distributed in wider PBH haloes of order hundreds of kpc, containing about 63% of objects and mass, coinciding with the sizes of galactic halos. We find at last high rates of close encounters of massive Black Holes (M∼1000M⊙), with ΓS=(1.2+5.9−0.9)×107yr−1Gpc−3 and mergers with ΓM=1337±41yr−1Gpc−3.
Highlights
One of the most pressing problems in cosmology is that of the nature of Dark Matter (DM), which was first suggested in the 1930s by Zwicky from the observation of motion anomalies in the Coma galaxy cluster in [1], and by Rubin in the 1970s from the observation of an excess velocity in the tails of galaxy rotation curves in [2]
Understanding the nature of Dark Matter remains one of the key questions in theoretical physics and cosmology and has resulted in a plethora of models ranging from weakly interacting massive particles (WIMPs), sterile neutrinos, axions, modifications of gravity like MOND and Primordial Black Holes (PBHs), see in [87,88] for recent reviews
We focus on the PBHs as it provides a model that connects the early time and late time physics and remains a plausible candidate for DM
Summary
One of the most pressing problems in cosmology is that of the nature of Dark Matter (DM), which was first suggested in the 1930s by Zwicky from the observation of motion anomalies in the Coma galaxy cluster in [1], and by Rubin in the 1970s from the observation of an excess velocity in the tails of galaxy rotation curves in [2]. It was mentioned in Section 6.1.3 that the trajectory stability of distant objects bound to the cluster or belonging to the ejecta sphere-of-influence is guaranteed in our simulations, as both the cluster and ejecta sphere-of-influence lives in isolation and the likelihood of an encounter that may transfer enough kinetic energy to overcome the cluster escape velocity is very low, as the ejected objects travel the cluster periphery where this far-off objects live very fast, and given that as the periods of these objects are very high. These numbers are large enough that eventually the volumes occupied by both the cluster and ejecta spheres-of-influence overlap, and so interaction between PBHs is no longer a remote possibility but a reality
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