Primordial Intermediate-mass Binary Black Holes as Targets for Space Laser Interferometers

TL;DR

This paper predicts that space-based laser interferometers like TianQin could detect primordial intermediate-mass black hole binaries formed in the early universe, characterized by unique features such as low spins and high redshifts.

Contribution

It introduces a model for primordial binary black hole formation and estimates detection rates for space-based interferometers, highlighting their potential to observe early universe black hole mergers.

Findings

Expected detection rate of a few to hundreds per year

Primordial IMBH mergers have low effective spins

Mergings can occur at redshifts greater than 20

Abstract

Primordial black holes (PBHs) with log-normal mass spectrum with masses up to $\sim 10^4-10^5 M_\odot$ can be created after QCD phase transition in the early Universe at $z\sim 10^{12}$ by the modified Affleck-Dine baryogenesis. Using a model binary PBH formation, the expected detection rate of such binary intermediate-mass PBHs by the TianQin space laser interferometer is calculated to be from a few to hundreds events per year for the assumed parameters of the PBH log-normal mass spectrum and abundance consistent with LIGO-Virgo-KAGRA results. Distinctive features of such primordial IMBH mergings are vanishingly small effective spins, possible high redshifts $z>20$ and lack of association with gas-rich regions or galaxies.