Primordial Black Hole Mergers as Probes of Dark Matter in Galactic Center

TL;DR

This paper investigates how primordial black hole mergers, influenced by dark matter spikes near galactic centers, can serve as observable probes to understand dark matter distribution and distinguish it from astrophysical black hole signals.

Contribution

It reveals a novel peaked structure in PBH merger rates at low redshifts due to dark matter spikes, applicable across various models, and highlights their potential as dark matter probes.

Findings

Peaked PBH merger rate at z ~ 5 linked to dark matter spikes.

Distinct redshift evolution allows differentiation from astrophysical black holes.

Effects are robust across different PBH mass functions and spike profiles.

Abstract

Primordial black holes (PBHs) from the early Universe that can contribute to dark matter (DM) abundance have been linked to gravitational wave observations. Super-massive black holes (SMBHs) at the centers of galaxies are expected to modify distribution of DM in their vicinity, and can result in highly concentrated DM spikes. We revisit PBH merger rates in the presence of DM spikes, tracking their history. We find novel peaked structure in the redshift-evolution of PBH merger rates at low redshifts around $z \sim 5$. These effects are generic and are present for distinct PBH mass functions and spike profiles, and also can be linked to peaked structure in redshift evolution of star formation rate. Redshift evolution characteristics of PBH merger rates can be distinguished from astrophysical black hole contributions and observable with gravitational waves, enabling them to serve as probes of DM in galactic centers.