Abstract
We review the current status of studies of the coalescence of binary neutron star systems. We begin with a discussion of the formation channels of merging binaries and we discuss the most recent theoretical predictions for merger rates. Next, we turn to the quasi-equilibrium formalisms that are used to study binaries prior to the merger phase and to generate initial data for fully dynamical simulations. The quasi-equilibrium approximation has played a key role in developing our understanding of the physics of binary coalescence and, in particular, of the orbital instability processes that can drive binaries to merger at the end of their lifetimes. We then turn to the numerical techniques used in dynamical simulations, including relativistic formalisms, (magneto-)hydrodynamics, gravitational-wave extraction techniques, and nuclear microphysics treatments. This is followed by a summary of the simulations performed across the field to date, including the most recent results from both fully relativistic and microphysically detailed simulations. Finally, we discuss the likely directions for the field as we transition from the first to the second generation of gravitational-wave interferometers and while supercomputers reach the petascale frontier.
Highlights
Binaries composed of neutron stars (NSs) and black holes (BHs) have long been of interest to astrophysicists
It is reassuring that most estimates of the neutron star–neutron star (NS-NS) and black hole–neutron star (BH-NS) merger rate, expressed either as a rate of mergers per Myr per “Milky Way equivalent galaxy” or as a predicted detection rate for LIGO and Virgo, agree to within 1 – 2 orders of magnitude, which is comparable to the typical uncertainties that remain once all possible sources of error are folded into a population synthesis model
It is possible to determine whether or not a pair of NSs with given parameters and specified equation of state (EOS) will form a BH or Hypermassive NS (HMNS) promptly after merger, and to estimate whether a HMNS will collapse on a dynamical timescale or one of the longer dissipative timescales
Summary
Binaries composed of neutron stars (NSs) and black holes (BHs) have long been of interest to astrophysicists. Even with the handful of observed sources to date, one may use this sample to place empirical limits on the expected rate of NS-NS mergers [143] and to constrain the many parameters that enter into population synthesis calculations [217]. With regard to the former, the very short merger timescale for J0737, τmerge = 85 Myr, makes it especially important for estimating the overall rate of NS-NS mergers since it is a priori very unlikely to detect a system with such a short lifetime. For a review focusing on BH-NS merger calculations, we encourage the reader to consult the recent work by Shibata and Taniguchi [284]
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