Mass Ejection from the Remnant of a Binary Neutron Star Merger: Viscous-radiation Hydrodynamics Study

By S. Fujibayashi, Kentaro Kiuchi, N. Nishimura, Y. Sekiguchi, M. Shibata. Astrophysical Journal, 2017

180 citations recorded by the source corpus.

We perform long-term general relativistic neutrino radiation hydrodynamics simulations (in axisymmetry) for a massive neutron star (MNS) surrounded by a torus, which is a canonical remnant formed after the binary neutron star merger. We take into account the effects of viscosity, which is likely to arise in the merger remnant due to magnetohydrodynamical turbulence. The viscous effect plays key roles for the mass ejection from the remnant in two phases of the evolution. In the first t ≲ 10 ms, a differential rotation state of the MNS is changed to a rigidly rotating state. A shock wave caused by the variation of its quasi-equilibrium state induces significant mass ejection of mass ∼(0.5–2.0) for the α-viscosity parameter of 0.01–0.04. For the longer-term evolution with ∼0.1–10 s, a significant fraction of the torus material is ejected. We find that the total mass of the viscosity-driven ejecta ( ) could dominate over that of the dynamical ejecta ( ). The electron fraction, Ye, of the ejecta is always high enough (Ye ≳ 0.25) that this post-merger ejecta is lanthanide-poor; hence, the opacity of the ejecta is likely to be ∼10–100 times lower than that of the dynamical ejecta. This indicates that the electromagnetic signal from the ejecta would be rapidly evolving, bright, and blue if it is observed from a small viewing angle (≲45°) for which the effect of the dynamical ejecta is minor.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/eaf7d7aaa2c02f1b6184e6fc93778eb1457c4886

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Citations in the corpus

Origin of the heaviest elements: The rapid neutron-capture process (2019, background): “3 (Metzger and Fernández, 2014; Lippuner et al., 2017; Fujibayashi et al., 2018).”
Long-term GRMHD simulations of neutron star merger accretion discs: implications for electromagnetic counterparts (2018, methodology): “This has been used as an argument for a non-zero lifetime of the HMNS in GW170817, which would irradiate the ejecta with neutrinos and increase the electron fraction (Metzger & Fernández 2014; Perego et al. 2014; Fujibayashi et al. 2018), resulting in a larger ejecta mass with Ye > 0.25.”
Binary Neutron Star Mergers: Mass Ejection, Electromagnetic Counterparts, and Nucleosynthesis (2018, background): “…material will become unbound from the remnant on longer timescales, due to magnetic effects and/or nuclear recombination (e.g., Fernández & Metzger 2013; Perego et al. 2014; Siegel & Metzger 2017; Fernández et al. 2019; Fujibayashi et al. 2018), which we cannot currently study with our simulations.”