In , Rosswog and Davies included a detailed neutrino leakage scheme in their calculations and also adopted the Shen EOS for several calculations, finding in a later paper  that the gamma-ray energy release is roughly 1048 erg, in line with previous results from other groups, but noting that the values would be significantly higher if temperatures in the remnant were higher, since the neutrino luminosity scales like a very high power of the temperature. These calculations also identified NS-NS mergers as likely SGRB candidates given the favorable geometry , and the possibility that the MRI in a HMNS remnant could dramatically boost magnetic fields on the sub-second timescales characterizing SGRBs . Rosswog and Liebendörfer  found that electron antineutrinos dominate the emission, as had Ruffert and Janka , though the exact thermodynamic and nuclear profiles were found to be somewhat sensitive to the properties of the EOS model. More recently, using the VULCAN 2-dimensional multi-group flux-limited-diffusion radiation hydrodynamics code  to evaluate slices taken from SPH calculations, Dessart et al.  found that neutrino heating of the remnant material will eject roughly from the system.
Price and Rosswog [233, 247] performed the first MHD simulation of merging NS-NS binaries using an SPH code that included magnetic field effects, finding that the Kelvin–Helmholtz unstable vortices formed at the contact surface between the two NSs could boost magnetic fields rapidly up to 1017 G. These results were not seen in GRMHD simulations, where gains in the magnetic field strength generated by dynamos were limited by the swamping of the vortex sheet at the surface of contact by rapidly infalling NS material that went on to form the eventual HMNS or BH . Longer-term simulations did note that shearing instabilities were able to support power-law, or perhaps even exponential, growth of the magnetic fields on longer timescales ( 10 s of ms), which augurs well for NS-NS mergers as the central engines of SGRBs .
An effort to identify potential observational differences between NSs and COs with quark-matter interiors has been led by Oechslin and collaborators. Using an SPH code with CF gravity, Oechslin et al. [210, 212] considered mergers of NSs with quark cores described by the MIT bag model [67, 102, 142], which have significantly smaller maximum masses than traditional NSs. They found the hybrid nuclear-quark EOS yielded higher ISCO frequencies for NSs with masses and slightly larger GW oscillation frequencies for any resulting merger remnant compared to purely hadronic EOS. Bauswein et al.  followed up this work by investigating whether “strangelets”, or small lumps of strange quark matter, would be ejected in sufficient amounts throughout the interstellar medium to begin the phase transition that would convert traditional hadronic NSs into strange stars. They determined that the total rate of strange matter ejection in NS-NS mergers could be as much as per year per galaxy or essentially zero depending on the parameters input into the MIT bag model, with the upper values clearly detectable by orbiting magnetic spectrometers such as the AMS-02 detector that was recently installed on the International Space Station [182, 148]. Further calculations concluded that the mergers of strange stars produce a much more tenuous halo than traditional NS mergers, more rapid formation of a BH, and higher frequency ringdown emission , as we show in Figure 17.
Oechslin, Janka, and Marek also analyzed a wide range of EOS models using their CF SPH code, finding that matter in spiral arms was typically cold and that the dynamics of the disk formed around a post-merger BH depends on the initial temperature assumed for the pre-merger NS . They also determined that the kHz GW emission peaks produced by HMNSs may help to constrain various parameters of the original NS EOS, especially its high-density behavior , with further updates to the prediction provided by Bauswein and Janka . Most recently, Stergioulas et al.  studied the effect of nonlinear mode couplings in HMNS oscillations, leading to the prediction of a triplet peak of frequencies being present or low mass () systems in the kHz range.
Living Rev. Relativity 15, (2012), 8
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