Detectability of Gravitational Waves from High-Redshift Binaries

TL;DR

This paper explores the potential of current and future gravitational-wave observatories to detect high-redshift supermassive black hole binaries, suggesting some could be observable across the universe, expanding search strategies.

Contribution

It demonstrates that certain supermassive black hole binaries are detectable at any redshift with current and future gravitational-wave detectors, challenging previous assumptions.

Findings

Supermassive binaries with masses >10^10 M_sun are detectable at any redshift.

Future arrays will detect less massive binaries at high redshifts.

Detection horizons depend on binary mass, detector sensitivity, and waveform modeling.

Abstract

Recent non-detection of gravitational-wave backgrounds from pulsar timing arrays casts further uncertainty on the evolution of supermassive black hole binaries. We study the capabilities of current gravitational-wave observatories to detect individual binaries and demonstrate that, contrary to conventional wisdom, some are in principle detectable throughout the Universe. In particular, a binary with rest-frame mass $\gtrsim10^{10}\,M_\odot$ can be detected by current timing arrays at arbitrarily high redshifts. The same claim will apply for less massive binaries with more sensitive future arrays. As a consequence, future searches for nanohertz gravitational waves could be expanded to target evolving high-redshift binaries. We calculate the maximum distance at which binaries can be observed with pulsar timing arrays and other detectors, properly accounting for redshift and using realistic binary waveforms.