Magnetic Field Configurations in Binary Neutron Star Mergers I: Post-merger Remnant and Disk

TL;DR

This paper uses advanced GRMHD simulations to study how initial magnetic field configurations, equations of state, and symmetry assumptions influence the magnetic and thermodynamic evolution of neutron star merger remnants and disks.

Contribution

It systematically investigates the effects of initial magnetic topology, EOS, and symmetry assumptions on post-merger magnetic field evolution using high-resolution GRMHD simulations.

Findings

Magnetic fields amplify rapidly after merger due to Kelvin-Helmholtz instability.

Initial magnetic topology influences field structure and amplification.

Enforcing equatorial symmetry affects turbulence development and magnetic evolution.

Abstract

We present a suite of general relativistic magnetohydrodynamic (GRMHD) simulations of binary neutron star (BNS) mergers performed with the code GR-Athena++. We investigate how a different initial magnetic field configuration, nuclear equation of state, or binary mass ratio affects the magnetic and thermodynamic evolution of the post-merger remnant and disk. We also analyze the impact of the commonly-assumed reflection (bitant) symmetry across the equatorial plane. Magnetic field amplification occurs shortly after the merger due to the Kelvin-Helmholtz instability; later, the field keeps evolving with a predominantly toroidal configuration due to winding and turbulence. The initial magnetic field topology leaves an imprint on the field structure and affects magnetic field amplification for the initial magnetic field values commonly assumed in the literature and the limited resolution of the simulations. Enforcing equatorial reflection symmetry partially suppresses the development of turbulence near the equatorial plane and impacts the post-merger magnetic field evolution. Stiffer EOSs produce larger, less compact remnants that may retain memory of the pre-merger strong poloidal field.