Multi-Messenger Astrophysics with Pulsar Timing Arrays

TL;DR

Pulsar timing arrays are close to detecting low-frequency gravitational waves from supermassive black hole binaries, enabling multi-messenger astronomy that combines gravitational and electromagnetic observations to advance astrophysics and cosmology.

Contribution

This paper discusses the potential of PTAs for multi-messenger detection of SMBHBs, highlighting upcoming surveys and the scientific breakthroughs expected in the next decade.

Findings

PTAs will detect low-frequency GWs from SMBHBs within a decade.

Electromagnetic surveys are identifying SMBHB candidates, aiding GW source localization.

Multi-messenger observations will revolutionize understanding of SMBH evolution and cosmology.

Abstract

Pulsar timing arrays (PTAs) are on the verge of detecting low-frequency gravitational waves (GWs) from supermassive black hole binaries (SMBHBs). With continued observations of a large sample of millisecond pulsars, PTAs will reach this major milestone within the next decade. Already, SMBHB candidates are being identified by electromagnetic surveys in ever-increasing numbers; upcoming surveys will enhance our ability to detect and verify candidates, and will be instrumental in identifying the host galaxies of GW sources. Multi-messenger (GW and electromagnetic) observations of SMBHBs will revolutionize our understanding of the co-evolution of SMBHs with their host galaxies, the dynamical interactions between binaries and their galactic environments, and the fundamental physics of accretion. Multi-messenger observations can also make SMBHBs 'standard sirens' for cosmological distance measurements out to $z\simeq0.5$. LIGO has already ushered in breakthrough insights in our knowledge of black holes. The multi-messenger detection of SMBHBs with PTAs will be a breakthrough in the years $2020-2030$ and beyond, and prepare us for LISA to help complete our views of black hole demographics and evolution at higher redshifts.