Anisotropic pressure and hyperons in neutron stars

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 ≤ 0.8 1 and Λ ≤ −1.15. 2 The radius of the corresponding neutron star at M =1.4 M ⊙ 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 ⊙ cannot rule out the presence of hyperons in the neutron star core.

Impact of phase transition from neutrons to hyperons in neutron star properties

“…Note that the equation of state obtained from Equation (1) while neutron star properties obtained by using Equation (4). First, we will see how g σ * Λ /g σN coupling constant variation affects the equation of state of neutron stars by using BSP parameter set.…”

“…In RMF model, the interaction among baryons is mediated by the exchange of meson fields. The total Lagrangian density for RMF model consists of a Lagrangian density of free baryons, free mesons, free leptons, and interactions where the corresponding Lagrangian density can be written as [4] …”

“…Coupling constants for nucleon are taken from Reference [4] and the couplings for vector meson with hyperon are obtained from SU(6) relations…”

Cracking on anisotropic neutron stars

“…For recent review about the status of this approach see Reference [7] and the references therein. Recently, the author of Reference [8] showed, if the isotropic assumption is relaxed by considering that the pressure in NS could be anisotropic, the maximal mass around 2.1M can be easily reached by adjusting anisotropic parameter of the anisotropic models. In the corresponding study, they used the anisotropic models which were proposed by Doneva-Yazadjiev (DY) [2] and Herrera-Barreto (HB) [3].…”

“…In the corresponding study, they used the anisotropic models which were proposed by Doneva-Yazadjiev (DY) [2] and Herrera-Barreto (HB) [3]. Reviews of the source of the appearance of pressure anisotropic in compact objects and the corresponding models used to accommodate pressure anisotropic for examples can be found in Reference [8,9] (see also the references therein). The recent investigation on the properties of anisotropic compact stars are reported for examples in Reference [8,2,3].…”