Neutron star mergers and how to study them

Abstract

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. 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. 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. 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. I then present the key observations necessary to advance our understanding of these sources, followed by the broad science this enables. I close with a discussion on the necessary future capabilities to fully utilize these enigmatic sources to understand our universe.

Quasi-universal behaviour of the threshold mass in unequal-mass, spinning binary neutron-star mergers

“…Given its impact on the electromagnetic counterpart, a particularly important prediction of the theoretical modelling has been the determination of whether the BNS underwent a prompt collapse at merger. The threshold mass discerning a prompt from a delayed collapse has been investigated thoroughly for irrotational binaries (see Baiotti & Rezzolla 2017;Burns 2020, for some reviews) using a number of EOSs. The natural expectation that the thresh-old mass can be parametrized in terms of the maximum mass of a nonrotating NS, M TOV (Bauswein et al 2013), has been refined by more advanced parametrizations (Koeppel et al 2019;Agathos et al 2019) and by incorporating the effect of asymmetric binary systems (Bauswein et al 2021).…”

The Compton Spectrometer and Imager Project for MeV Astronomy

“…A COSI launch in 2025 would mean that it is observing when A+ generation gravitational wave detectors are planned to be in operation. In the A+ era, the joint BNS-GRB detection range is 620 Mpc (see Table 4 in [4]) for the three LIGO interferometers, which takes a near face-on distribution averaged over the full-sky. A distance of 620 Mpc corresponds to = 0.13, and 14% of short GRBs are within that redshift [4].…”

“…In the A+ era, the joint BNS-GRB detection range is 620 Mpc (see Table 4 in [4]) for the three LIGO interferometers, which takes a near face-on distribution averaged over the full-sky. A distance of 620 Mpc corresponds to = 0.13, and 14% of short GRBs are within that redshift [4]. Thus, we would predict joint COSI and gravitational wave detections of 4.2-5.6 events during the 2 year COSI prime mission.…”

Electromagnetic Precursors of Short Gamma-Ray Bursts as Counterparts of Gravitational Waves

“…In theory, many EM signals are expected for the NS merger. The observation and theory of SGRBs, afterglows, and kilonova were summarized in many reviews [27][28][29][30][31][32]. However, little attention has been placed on the pre-merger EM radiation.…”