Compact Binary Merger Rate in Dark-Matter Spikes

TL;DR

This paper investigates how dark-matter spikes around supermassive black holes influence the merger rate of compact binaries, finding that ellipsoidal-collapse models can enhance merger rates and that primordial black hole binary rates align with LIGO-Virgo observations.

Contribution

It introduces calculations of merger rates in dark-matter spikes considering different halo collapse models, highlighting the impact of ellipsoidal collapse on merger rate enhancement.

Findings

Ellipsoidal-collapse models increase merger rate predictions.

Primordial black hole binary merger rates match LIGO-Virgo data.

Primordial black hole-neutron star merger rates are inconsistent with observations.

Abstract

Nowadays, the existence of supermassive black holes (SMBHs) in the center of galactic halos is almost confirmed. An extremely dense region referred to as dark-matter spike is expected to form around central SMBHs as they grow and evolve adiabatically. In this work, we calculate the merger rate of compact binaries in dark-matter spikes while considering halo models with spherical and ellipsoidal collapses. Our findings exhibit that ellipsoidal-collapse dark matter halo models can potentially yield the enhancement of the merger rate of compact binaries. Finally, our results confirm that the merger rate of primordial black hole binaries is consistent with the results estimated by the LIGO-Virgo detectors, while such results can not be realized for primordial black hole-neutron star binaries.