Structure formation with primordial black holes: collisional dynamics, binaries, and gravitational waves

TL;DR

This paper presents the first detailed simulations of primordial black hole dark matter, incorporating collisional effects, gravitational wave emission, and mergers, revealing complex dynamical behaviors and implications for gravitational wave observations.

Contribution

It introduces comprehensive cosmological simulations of PBH dark matter that include collisional dynamics, post-Newtonian corrections, and merger processes, advancing understanding of PBH structure formation.

Findings

PBH halos evolve due to collisional effects

Formation of a hot PBH component observed

Gravitational wave emission exceeds current experimental limits

Abstract

Primordial black holes (PBHs) could compose the dark matter content of the Universe. We present the first simulations of cosmological structure formation with PBH dark matter that consistently include collisional few-body effects, post-Newtonian orbit corrections, orbital decay due to gravitational wave emission, and black-hole mergers. We carefully construct initial conditions by considering the evolution during radiation domination as well as early-forming binary systems. We identify numerous dynamical effects due to the collisional nature of PBH dark matter, including evolution of the internal structures of PBH halos and the formation of a hot component of PBHs. We also study the properties of the emergent population of PBH binary systems, distinguishing those that form at primordial times from those that form during the nonlinear structure formation process. These results will be crucial to sharpen constraints on the PBH scenario derived from observational constraints on the gravitational wave background. Even under conservative assumptions, the gravitational radiation emitted over the course of the simulation appears to exceed current limits from ground-based experiments, but this depends on the evolution of the gravitational wave spectrum and PBH merger rate toward lower redshifts.