Merger rates in primordial black hole clusters without initial binaries

Abstract

Primordial black holes formed through the collapse of cosmological density fluctuations have been hypothesised as contributors to the dark matter content of the Universe. At the same time, their mergers could contribute to the recently observed population of gravitational-wave sources. We investigate the scenario in which primordial black holes form binaries at late times in the Universe. Specifically, we re-examine the mergers of primordial black holes in small clusters of ~30 objects in the absence of initial binaries. Binaries form dynamically through Newtonian gravitational interactions. These binaries act as heat sources for the cluster, increasing the cluster's velocity dispersion, which inhibits direct mergers through gravitational-wave two-body captures. Meanwhile, three-body encounters of tight binaries are too rare to tighten binaries sufficiently to allow them to merge through gravitational-wave emission. We conclude that in the absence of initial binaries, merger rates of primordial black holes in the Bird et al. (2016) initial cluster configuration are at least an order of magnitude lower than previously suggested, which makes gravitational-wave detections of such sources improbable.

8 pages, 4 figures

References in corpus (3)

• Constraints on Primordial Black Holes
• Primordial Black Holes as Dark Matter
• The merger rate of primordial-black-hole binaries

Cited by in corpus (16)

• Constraints on Primordial Black Holes
• Hierarchical mergers of stellar-mass black holes and their gravitational-wave signatures
• Rates of Compact Object Coalescences
• Detection of Early-Universe Gravitational Wave Signatures and Fundamental Physics
• Signs of eccentricity in two gravitational-wave signals may indicate a sub-population of dynamically assembled binary black holes
• Hunt for Light Primordial Black Hole Dark Matter with Ultra-High-Frequency Gravitational Waves
• The Minimum Testable Abundance of Primordial Black Holes at Future Gravitational-Wave Detectors
• Measuring dark matter spikes around primordial black holes with Einstein Telescope and Cosmic Explorer
• Primordial black holes and gravitational waves in nonstandard cosmologies
• Primordial black hole mergers from three-body interactions
• Observational Support for Massive Black Hole Formation Driven by Runaway Stellar Collisions in Galactic Nuclei
• Effect of a High-Precision Semi-Analytical Mass Function on the Merger Rate of Primordial Black Holes in Dark Matter Halos
• Feeding plankton to whales: high-redshift supermassive black holes from tiny black hole explosions
• The Merger Rate of Black Holes in a Primordial Black Hole Cluster
• Dynamics and merger rate of primordial black holes in a cluster
• The Maximal Gravitational Wave Signal from Asteroid-Mass Primordial Black Hole Mergers At Resonant Microwave Cavities