When available, we reference manuscripts that contain more detailed discussions. Several papers have been written on science beyond astrophysics enabled by observations of these events. Several papers and reviews on the astrophysics of NS mergers have been written, both before and after GW170817. Binary Neutron Star (BNS) and Neutron Star–Black Hole (NSBH) mergers, collectively referred to here as NS mergers, will be important astrophysical multimessenger sources for the foreseeable future. The modern era of time domain, multimessenger astrophysics will hopefully result in multiple detections of multiple source classes with multiple messengers. 2017d), and likely neutrinos and photons from a flaring blazar (Aartsen et al. 1987), gravitational waves and photons from a binary neutron star merger (this event Abbott et al. There have been only three convincing multimessenger detections of individual astrophysical sources: neutrinos and photons from the core-collapse supernova SN 1987A (Hirata et al. For decades, the scientific promise of these sources has been known, and the first event certainly met expectations with, on average, more than three papers written per day over the first two years. These discoveries culminated in a suite of papers published only two months after the first detection, with contributions from thousands of astronomers and astrophysicists, ushering in the new era of GW multimessenger astrophysics. 2017) that has been detected until more than two years later. 2017), the theoretically predicted radioactively-powered kilonova, whose precise location enabled the identification of “off-axis” afterglow emission (Troja et al. 2017d), which resulted in six independent detections of AT2017gfo (Coulter et al.
This joint detection resulted in the greatest follow-up observation campaign in the history of transient astrophysics (Abbott et al. 2015) and the gamma rays as GRB 170817A (Goldstein et al. 2015) and Advanced Virgo (Acernese et al. 2017c) by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO Aasi et al. 2017b): the GWs observed as GW170817 (Abbott et al. On August 17th, 2017 the messengers arrived at Earth (Abbott et al. As the messengers neared Sirius the Fermi Space Telescope was launched after they passed Alpha Centauri the Advanced Gravitational wave (GW) interferometers were turned on for the first time. Two Neutron Stars (NSs) from the galaxy NGC 4993 merged, emitting two messengers that traveled together from the age of dinosaurs through the age of civilization. I close with a discussion on the necessary future capabilities to fully utilize these enigmatic sources to understand our universe. I then present the key observations necessary to advance our understanding of these sources, followed by the broad science this enables. This review begins with a summary of our current knowledge of these events, the expected observational signatures, and estimated detection rates for the next decade. Uncovering this science requires vast observational resources, unparalleled coordination, and advancements in theory and simulation, which are constrained by our current understanding of nuclear, atomic, and astroparticle physics. Studies of these events enable unique insights into astrophysics, particles in the ultrarelativistic regime, the heavy element enrichment history through cosmic time, cosmology, dense matter, and fundamental physics. Neutron star mergers are the canonical multimessenger events: they have been observed through photons for half a century, gravitational waves since 2017, and are likely to be sources of neutrinos and cosmic rays.