In [244], 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 [248] 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 [249], and the possibility
that the MRI in a HMNS remnant could dramatically boost magnetic fields on the sub-second
timescales characterizing SGRBs [250]. Rosswog and Liebendörfer [246] found that electron
antineutrinos
dominate the emission, as had Ruffert and Janka [252
], 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 [173] to evaluate slices taken from SPH calculations, Dessart et al. [82
]
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 [117
]. 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 [241
].
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. [34] 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 [35
], 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 [209]. 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 [208], with further updates to the
prediction provided by Bauswein and Janka [32]. Most recently, Stergioulas et al. [296] 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.
http://www.livingreviews.org/lrr-2012-8 |
Living Rev. Relativity 15, (2012), 8
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