Magnetohydrodynamic simulations of self-consistent rotating neutron stars with mixed poloidal and toroidal magnetic fields

TL;DR

This study conducts the first full general relativistic magnetohydrodynamic simulations of rotating neutron stars with complex magnetic fields, revealing their stability, rotational dynamics, and ejecta characteristics.

Contribution

It introduces the first comprehensive GRMHD simulations of rotating neutron stars with mixed magnetic fields, exploring their stability and evolution.

Findings

All models develop instabilities and succumb to them.

Differential rotation occurs and then reverts to uniform rotation.

Rapidly rotating magnetars eject matter potentially observable as kilonovae.

Abstract

We perform the first magnetohydrodynamic simulations in full general relativity of self-consistent rotating neutron stars (NSs) with ultrastrong mixed poloidal and toroidal magnetic fields. The initial uniformly rotating NS models are computed assuming perfect conductivity, stationarity, and axisymmetry. Although the specific geometry of the mixed field configuration can delay or accelerate the development of various instabilities known from analytic perturbative studies, all our models finally succumb to them. Differential rotation is developed spontaneously in the cores of our magnetars which, after sufficient time, is converted back to uniform rotation. The rapidly rotating magnetars show a significant amount of ejecta, which can be responsible for transient kilonova signatures. However no highly collimated, helical magnetic fields or incipient jets, which are necessary for gamma-ray bursts, arise at the poles of these magnetars by the time our simulations are terminated.