Constraining the Surface Curvature of an Anisotropic Neutron Star

TL;DR

This paper investigates how pressure anisotropy affects the surface curvature of neutron stars, analyzing various macroscopic properties and their relations using observational data to constrain theoretical models.

Contribution

It introduces a scalar pressure anisotropy model to quantify anisotropy effects on neutron star properties, including surface curvature, and explores universal relations with observational constraints.

Findings

Pressure anisotropy significantly influences surface curvature.

Universal relations between surface curvature, tidal deformability, and moment of inertia are established.

Constraints on surface curvature are derived from GW170817 data.

Abstract

The anisotropy of pressure arises due to the various complex phenomena that happen inside the neutron star (NS). In this study, we calculate the degree of anisotropy inside the NS using the scalar pressure anisotropy model. Macroscopic properties such as mass, radius, compactness, redshift, tidal deformability, the moment of inertia, and surface curvature (SC) are computed for the anisotropic NS with the equation of states spanning from relativistic to nonrelativistic cases. The variation of SC as the functions of the above-mentioned quantities are computed by changing the degree of anisotropy. Pressure anisotropy has significant effects on the magnitude of SC. The universal relations between the canonical SC$-\Lambda$ and SC$-\bar{I}$ are studied. From the GW170817 tidal deformability data constraints on SC are found to be SC$_{1.4}(10^{14}) = 3.44_{-1.0}^{+0.4}, 2.85_{-1.20}^{+0.62}, \ {\rm and} \ 2.52_{-1.02}^{+0.61}$ for $\lambda_{\rm BL} = 0.0, 1.0$, and $2.0$ respectively.