Global simulations of strongly magnetized remnant massive neutron stars formed in binary neutron star mergers

TL;DR

This study uses high-resolution general-relativistic magnetohydrodynamics simulations to investigate magnetic field amplification and turbulence in remnant massive neutron stars formed after binary neutron star mergers.

Contribution

It provides detailed insights into magnetic field amplification mechanisms and turbulence sustainability in neutron star remnants with unprecedented resolution.

Findings

Kelvin-Helmholtz instability can amplify magnetic energy to about 1% of thermal energy.

Magnetorotational instability sustains magneto-turbulence with an effective viscosity of 0.01-0.02 in certain regions.

Current grid resolution is insufficient to sustain turbulence in denser regions of the remnant.

Abstract

We perform a general-relativistic magnetohydrodynamics simulation for $\approx 30$ ms after merger of a binary neutron star to a remnant massive neutron star (RMNS) with a high spatial resolution of the finest grid resolution $12.5$ m. First, we estimate that the Kelvin-Helmholtz instability at merger could amplify the magnetic-field energy up to $\sim 1\%$ of the thermal energy. Second, we find that the magnetorotational instability in the RMNS envelope and torus with $\rho < 10^{13}~{\rm g~cm^{-3}}$ sustains magneto-turbulent state and the effective viscous parameter in these regions is likely to converge to $\approx 0.01$--$0.02$ with respect to the grid resolution. Third, the current grid resolution is not still fine enough to sustain magneto-turbulent state in the RMNS with $\rho \ge 10^{13}~{\rm g~cm^{-3}}$.