Kepler frequency and moment of inertia of rotating neutron stars with chaotic magnetic field

TL;DR

This study computes the effects of chaotic magnetic fields on the Kepler frequency and moment of inertia of rotating neutron stars, revealing magnetic field strength influences these properties and aligning results with observational constraints.

Contribution

It introduces a model incorporating chaotic magnetic fields into neutron star structure calculations, analyzing their impact on rotational properties using the Hartle-Thorne formalism.

Findings

Magnetic field strength increases the Kepler frequency of neutron stars.

Moment of inertia is minimally affected at low masses but increases with magnetic field at higher masses.

Results align with observational data from pulsar measurements, gravitational waves, and NICER.

Abstract

Rotating neutron stars (NSs) are crucial objects of study, as our understanding of them relies significantly on observational data from these rotating stars. Observations suggest that the magnetic fields of NSs range from approximately $10^{8-15}$ G. In this work, we compute the Kepler frequency and moment of inertia for rotating NSs under the influence of a chaotic magnetic field. We utilize an equation of state (EOS) incorporating nuclei in the crust and hyperons in the core, with the Hartle-Thorne formalism applied to address the rotational aspects. A magnetic field ansatz is selected, in which the magnetic field is coupled to the energy density. To examine the impact of a chaotic magnetic field on the Kepler frequency and moment of inertia, we vary the magnetic field strength. Our results indicate that an increase in magnetic field strength enhances the Kepler frequency of rotating NSs. For the moment of inertia, the effect of magnetic field variation is minimal at lower masses but becomes more pronounced as the mass exceeds $M=0.5 M_\odot$, where moment of inertia increases with increasing magnetic field. Furthermore, our results for the moment of inertia comply with constraint derived from pulsar mass measurements, data from gravitational wave events GW170817 and GW190425, and X-ray observations of emission from hotspots on NS surfaces measured by NICER.