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 ≳1010M⊙ 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.
@article{arxiv.1512.04950,
title = {Detectability of Gravitational Waves from High-Redshift Binaries},
author = {Pablo A. Rosado and Paul D. Lasky and Eric Thrane and Xingjiang Zhu and Ilya Mandel and Alberto Sesana},
journal= {arXiv preprint arXiv:1512.04950},
year = {2016}
}