Constraining the central magnetic field of magnetars

TL;DR

This paper investigates how extremely strong magnetic fields inside magnetars influence their internal matter, mass-radius relation, and stability, establishing an upper limit around 10^{19} G for the central magnetic field.

Contribution

It models neutron star matter with hyperons under strong magnetic fields, revealing the impact on star properties and identifying an upper magnetic field limit for stability.

Findings

Magnetic fields above 10^{17} G significantly affect neutron star matter.

Anisotropy in matter becomes prominent at high magnetic fields.

Matter becomes unstable when the magnetic field approaches 10^{19} G.

Abstract

The magnetars are believed to be highly magnetized neutron stars having surface magnetic field 10^{14} - 10^{15} G. It is believed that at the center, the magnetic field may be higher than that at the surface. We study the effect of the magnetic field on the neutron star matter. We model the nuclear matter with the relativistic mean field approach considering the possibility of appearance of hyperons at higher density. We find that the effect of magnetic field on the matter of neutron stars and hence on the mass-radius relation is important, when the central magnetic field is atleast of the order of 10^{17} G. Very importantly, the effect of strong magnetic field reveals anisotropy to the system. Moreover, if the central field approaches 10^{19} G, then the matter becomes unstable which limits the maximum magnetic field at the center of magnetars.