The astrophysics of nanohertz gravitational waves

• DOI: 10.1007/s00159-019-0115-7
• Publication Date: 2019-06-18T17:02:33Z
• Authors: Sarah Burke-Spolaor; Stephen R. Taylor; Maria Charisi; Timothy Dolch; Jeffrey S. Hazboun; A. Miguel Holgado; Luke Zoltan Kelley; T. Joseph W. Lazio; Dustin R. Madison; Natasha McMann; Chiara M. F. Ming...; Alexander Rasskazov; Xavier Siemens; Joseph J. Simon; Tristan L. Smith
• Keywords: High Energy Astrophysical Phenomena (astro-ph.HE); Evolution; Physics; FOS: Physical sciences; Neutron; General Relativity and Quantum Cosmology (gr-qc); Black hole physics; Galaxies; 530; Stars; Astrophysics - Astrophysics of Galaxies; 01 natural sciences; 7. Clean energy; General Relativity and Quantum Cosmology; Gravitational waves; Cosmology; Miscellaneous; QC Physics / fizika; Astrophysics of Galaxies (astro-ph.GA); 0103 physical sciences; Astrophysics - High Energy Astrophysical Phenomena

Pulsar timing array (PTA) collaborations in North America, Australia, and Europe, have been exploiting the exquisite timing precision of millisecond pulsars over decades of observations to search for correlated timing deviations induced by gravitational waves (GWs). PTAs are sensitive to the frequency band ranging just below 1 nanohertz to a few tens of microhertz. The discovery space of this band is potentially rich with populations of inspiraling supermassive black-holes binaries, decaying cosmic string networks, relic post-inflation GWs, and even non-GW imprints of axionic dark matter. This article aims to provide an understanding of the exciting open science questions in cosmology, galaxy evolution, and fundamental physics that will be addressed by the detection and study of GWs through PTAs. The focus of the article is on providing an understanding of the mechanisms by which PTAs can address specific questions in these fields, and to outline some of the subtleties and difficulties in each case. The material included is weighted most heavily towards the questions which we expect will be answered in the near-term with PTAs; however, we have made efforts to include most currently anticipated applications of nanohertz GWs.<br/>Accepted to The Astronomy and Astrophysics Review (A&ARv)<br/>