Maximum redshift of gravitational wave merger events

TL;DR

Future advanced gravitational wave detectors could observe events at very high redshifts, and analyzing their rate and distribution can reveal whether they originate from primordial black holes or non-Gaussian density fluctuations.

Contribution

This paper demonstrates that high-redshift gravitational wave events can distinguish between primordial black holes and non-Gaussian density fluctuations as their sources.

Findings

Detection of >1 event/year at z > 40 implies non-Gaussian fluctuations or primordial black holes.

Redshift distribution of merger rate can identify the nature of the sources.

High-redshift GW events can probe early universe conditions.

Abstract

Future generation of gravitational wave detectors will have the sensitivity to detect gravitational wave events at redshifts far beyond any detectable electromagnetic sources. We show that if the observed event rate is greater than one event per year at redshifts z > 40, then the probability distribution of primordial density fluctuations must be significantly non-Gaussian or the events originate from primordial black holes. The nature of the excess events can be determined from the redshift distribution of the merger rate.