Anisotropic neutron stars in $R^2$ gravity

TL;DR

This paper investigates anisotropic neutron stars in $R^2$ gravity, showing that anisotropy allows for stiffer equations of state to match observations and predicts observable differences from general relativity.

Contribution

It introduces the role of anisotropy in neutron star modeling within $R^2$ gravity, expanding the range of compatible equations of state and identifying potential observational signatures.

Findings

Anisotropy enables stiffer equations of state to fit observational data.

Neutron stars in $R^2$ gravity exhibit distinguishable accretion disk signatures.

Soft equations of state are only compatible with observations in isotropic models.

Abstract

We consider static neutron stars within the framework of $R^2$ gravity. The neutron fluid is described by three different types of realistic equations of state (soft, moderately stiff, and stiff). Using the observational data on the neutron star mass-radius relation, it is demonstrated that the characteristics of the objects supported by the isotropic fluid agree with the observations only if one uses the soft equation of state. We show that the inclusion of the fluid anisotropy enables one also to employ more stiff equations of state to model configurations that will satisfy the observational constraints sufficiently. Also, using the standard thin accretion disk model, we demonstrate potentially observable differences, which allow us to distinguish the neutron stars constructed within the modified gravity framework from those described in Einstein's general relativity.