Gyromagnetic ratio of rapidly rotating compact stars in general relativity

TL;DR

This study numerically investigates the gyromagnetic ratio of rapidly rotating, charged neutron stars in general relativity, revealing its proportionality to star compactness and limitations in achieving certain theoretical values.

Contribution

It provides new numerical insights into how the gyromagnetic ratio depends on star properties and rotation, under specific assumptions in relativistic star models.

Findings

Gyromagnetic ratio is proportional to star compactness M/R.

Little dependence of g on angular velocity.

Achieving g=2 is unlikely for low charge-to-mass ratio models.

Abstract

We numerically calculate equilibrium configurations of uniformly rotating and charged neutron stars, in the case of insulating material and neglecting the electromagnetic forces acting on the equilibrium of the fluid. This allows us to study the behaviour of the gyromagnetic ratio for those objects, when varying rotation rate and equation of state for the matter. Under the assumption of low charge and incompressible fluid, we find that the gyromagnetic ratio is directly proportional to the compaction parameter M/R of the star, and very little dependent on its angular velocity. Nevertheless, it seems impossible to have g=2 for these models with low charge-to-mass ratio, where matter consists of a perfect fluid and where the collapse limit is never reached.