High resolution numerical relativity simulations for the merger of binary magnetized neutron stars

Abstract

We perform high-resolution magnetohydrodynamics simulations of binary neutron star mergers in numerical relativity on the Japanese supercomputer K. The neutron stars and merger remnants are covered by a grid spacing of 70 m, which yields the highest-resolution results among those derived so far. By an in-depth resolution study, we clarify several amplification mechanisms of magnetic fields during the binary neutron star merger for the first time. First, the Kelvin-Helmholtz instability developed in the shear layer at the onset of the merger significantly amplifies the magnetic fields. A hypermassive neutron star (HMNS) formed after the merger is then subject to the nonaxisymmetric magnetorotational instability, which amplifies the magnetic field in the HMNS. These two amplification mechanisms cannot be found with insufficient-resolution runs. We also show that the HMNS eventually collapses to a black hole surrounded by an accretion torus which is strongly magnetized at birth. PACS numbers: 04.25.D-, 04.30.-w, 04.40.Dg

Dynamical mass ejection from the merger of asymmetric binary neutron stars: Radiation-hydrodynamics study in general relativity

“…Then, the geometrical thickness of the tori will be increased, and possibly, an outflow that ejects the matter from the outer part of the tori could be launched [31,[35][36][37][38]. The total rest mass of the ejected matter could reach 10% of the initial torus mass, according to the previous studies.…”

“…[31]). Thus, for a plausible value of α v ∼ 0.01, this system is a candidate for the central engine of short-hard gamma-ray bursts with the duration less than one second, like GRB 130603B [11] (see also Sec.…”

Dynamical mass ejection from binary neutron star mergers: Radiation-hydrodynamics study in general relativity

“…Also, we did not continue our simulations beyond 30-40 ms after the onset of merger. For the longer time scales, magnetohydrodynamic processes [41], viscous heating, and nuclear recombination [42] could be important. Self-consistent studies of these effects in the BNS merger also have to be done in the future.…”

The Fate of the Compact Remnant in Neutron Star Mergers

“…In the past decade, the number of hydrodynamic simulations of NS-NS and BH-NS mergers has grown considerably (Foucart et al 2010(Foucart et al , 2011(Foucart et al , 2015Foucart 2012;Korobkin et al 2012;Hotokezaka et al 2013;Kyutoku et al 2013;Bauswein et al 2014;Kiuchi et al 2014;Radice et al 2014;Shibata et al 2014;Takami et al 2014). Although these models are becoming increasingly sophisticated, most of the current models include only a subset of the physics needed to model these objects: hydrodynamics, neutrino transport (or at least neutrino energy losses), nuclear equations of state, magnetic fields, and general relativity.…”