Anisotropic pressure and hyperons in neutron stars

TL;DR

This paper investigates how anisotropic pressure influences neutron star properties with hyperons, showing it increases the equation of state stiffness and affects maximum mass predictions, aligning with recent observations.

Contribution

It introduces an extended relativistic mean field model to analyze anisotropic pressure effects on hyperonic neutron stars, highlighting the impact on maximum mass and radius.

Findings

Anisotropic pressure increases EOS stiffness.

Maximum neutron star mass can exceed 2.1 solar masses.

Neutron star radius at 1.4 solar masses is over 13 km.

Abstract

We study the effects of anisotropic pressure on properties of the neutron stars with hyperons inside its core within the framework of extended relativistic mean field. It is found that the main effects of anisotropic pressure on neutron star matter is to increase the stiffness of the equation of state, which compensates for the softening of the EOS due to the hyperons. The maximum mass and redshift predictions of anisotropic neutron star with hyperonic core are quite compatible with the result of recent observational constraints if we use the parameter of anisotropic pressure model $h \le 0.8$[1] and $\Lambda \le -1.15$ [2]. The radius of the corresponding neutron star at $M$=1.4 $M_\odot$ is more than 13 km, while the effect of anisotropic pressure on the minimum mass of neutron star is insignificant. Furthermore, due to the anisotropic pressure in the neutron star, the maximum mass limit of higher than 2.1 $M_\odot$ cannot rule out the presence of hyperons in the neutron star core.