AthenaK Simulations of Magnetized Binary Neutron Star Mergers

TL;DR

This paper presents advanced numerical simulations of magnetized binary neutron star mergers using AthenaK, revealing magnetic field amplification and funnel formation, but no magnetically-dominated outflow due to baryonic pollution.

Contribution

First detailed AthenaK simulations of magnetized neutron star mergers with adaptive mesh refinement and realistic physics.

Findings

Magnetic fields are amplified during merger.

A magnetized funnel forms in the remnant.

No magnetically-dominated outflow observed due to baryonic pollution.

Abstract

We present new numerical-relativity simulations of a magnetized binary neutron star merger performed with AthenaK. The simulations employ a temperature- and composition-dependent tabulated nuclear equation of state, with initially dipolar fields with a maximum initial strength of ${\sim}10^{16}\ {\rm G}$ which extend outside the stars. We employ adaptive mesh refinement and consider three grid resolutions, with grid spacing down to $\Delta x_{\rm min} \simeq 92\ {\rm m}$ in the most refined region. When comparing the two highest resolution simulations, we find orbital dephasing of over 7 orbits until merger of only $0.06$ radians. The magnetic field is amplified during the merger and we observe the formation of a magnetized funnel in the polar region of the remnant. Simulations are continued until about $30$ milliseconds after merger. However, due to significant baryonic pollution, the binary fails to produce a magnetically-dominated outflow. Finally, we discuss possible numerical and physical effects that might alter this outcome.