Gravitational Wave Signals from the First Massive Black Hole Seeds

TL;DR

This paper predicts gravitational wave signals from early massive black hole seeds formed by stellar collapse, suggesting LISA could detect these events and thus constrain models of black hole seed formation in the early Universe.

Contribution

It introduces the first in-situ merger rate estimates for massive black hole seeds from stellar collapse, linking gravitational wave signals to early black hole formation models.

Findings

LISA may detect 0.6 mergers per year from high-redshift massive black hole seeds.

Non-detection can constrain seed abundance, multiplicity, and coalescence times.

Gravitational waves can serve as probes of early Universe black hole formation processes.

Abstract

Recent numerical simulations reveal that the isothermal collapse of pristine gas in atomic cooling haloes may result in stellar binaries of supermassive stars with $M_* \gtrsim 10^4\ \mathrm{M}_{\odot}$. For the first time, we compute the in-situ merger rate for such massive black hole remnants by combining their abundance and multiplicity estimates. For black holes with initial masses in the range $10^{4-6} \ \mathrm{M}_{\odot}$ merging at redshifts $z \gtrsim 15$ our optimistic model predicts that LISA should be able to detect 0.6 mergers per year. This rate of detection can be attributed, without confusion, to the in-situ mergers of seeds from the collapse of very massive stars. Equally, in the case where LISA observes no mergers from heavy seeds at $z \gtrsim 15$ we can constrain the combined number density, multiplicity, and coalesence times of these high-redshift systems. This letter proposes gravitational wave signatures as a means to constrain theoretical models and processes that govern the abundance of massive black hole seeds in the early Universe.