Effects of Strong Magnetic Fields on Neutron Star Structure

TL;DR

This paper investigates how strong magnetic fields influence the structure and maximum mass of static neutron stars, revealing that magnetic effects can lead to higher maximum masses than rotation and cause off-center density peaks.

Contribution

It introduces a new analysis of static neutron star configurations with poloidal magnetic fields, showing increased maximum masses and off-center density maxima across various equations of state.

Findings

Magnetic fields can prevent static configurations when sufficiently strong.

Maximum mass with magnetic fields exceeds that of uniformly rotating stars.

Configurations often feature off-center density maxima.

Abstract

We study static neutron stars with poloidal magnetic fields and a simple class of electric current distributions consistent with the requirement of stationarity. For this class of electric current distributions, we find that magnetic fields are too large for static configurations to exist when the magnetic force pushes a sufficient amount of mass off-center that the gravitational force points outward near the origin in the equatorial plane. (In our coordinates an outward gravitational force corresponds to $\partial\ln g_{tt}/\partial r>0$, where $t$ and $r$ are respectively time and radial coordinates and $g_{tt}$ is coefficient of $dt^2$ in the line element.) For the equations of state (EOSs) employed in previous work, we obtain configurations of higher mass than had been reported; we also present results with more recent EOSs. For all EOSs studied, we find that the maximum mass among these static configurations with magnetic fields is noticeably larger than the maximum mass attainable by uniform rotation, and that for fixed values of baryon number the maximum mass configurations are all characterized by an off-center density maximum.