Dark Matter Simulations with Primordial Black Holes in the Early Universe

TL;DR

This study uses cosmological simulations to analyze primordial black hole formation, disruption, and mergers, providing insights consistent with gravitational wave observations and constraints on dark matter composition.

Contribution

It introduces a comprehensive simulation framework to study PBH pair dynamics and merger probabilities, accounting for dark matter effects and numerical stability.

Findings

PBH merger rates align with LIGO constraints.

Dark matter halo formation influences PBH pair stability.

Numerical errors impact the assessment of bound pair stability.

Abstract

Primordial Black Holes (PBH) with masses of order $10-30 M_\odot$ have been proposed as a possible explanation of the gravitational waves emission events recently discovered by the LIGO observatory. If true, then PBHs would constitute a sizeable fraction of the dark matter component in the Universe. Using a series of cosmological N-body simulations which include both dark matter and a variable fraction of PBHs ranging from $f_{PBH} = 10^{-4}$ to $f_{PBH} = 1$, we analyse the processes of formation and disruption of gravitationally bound PBH pairs, as well as the merging of both bound and unbound pairs, and estimate the probabilities of such events. We show that they are in good agreement with the constrains to the PBH abundance obtained by the LIGO and other research groups. We find that pair stability, while being a main factor responsible for the merger rate, is significantly affected by the effects of dark matter halo formation and clustering. As a side result, we also evaluate the effects of numerical errors in the stability of bound pairs, which can be useful for future research using this methodology.