Properties of neutron stars and strangeness-mixed stars from a pion mean-field approach

TL;DR

This paper explores the properties of neutron stars and strangeness-mixed stars using a pion mean-field approach, analyzing their internal structure, mass-radius relations, and the effects of strangeness content on their equations of state.

Contribution

It introduces a pion mean-field based model to study neutron stars and hyperon stars, providing new insights into their internal densities and mass-radius relations.

Findings

Central densities of neutron stars range from 3 to 4 times nuclear saturation density.

Increasing the slope parameter results in larger radii for neutron stars.

Strangeness content softens the equation of state and increases central densities.

Abstract

We investigate the properties of the static neutron stars and strangeness-mixed stars, based on the equations of state derived from a pion mean-field approach. Using the empirical data on the pion-nucleus scattering and bulk properties of nuclear matter, we have already fixed all the parameters in a previous work, where the nucleons and hyperons were shown to be modified in various nuclear medium. In the current work, we first examine the energy and pressure inside a neutron star. We show that the central densities in various neutron stars vary within the range of $(3-4)\rho_0$, where $\rho_0$ is the normal nuclear matter density. The mass-radius relations are obtained and discussed. As the slope parameter for neutron matter increases, the radii of the neutron stars increase with their masses fixed. We also study the strangeness-mixed stars or the hyperon stars using the same sets of the parameters. As the strangeness content of strange matter increases, the binding energy per nucleon is saturated and the corresponding equation of state becomes softened. Consequently, the central densities of the strangeness-mixed stars increase. Assuming that recently observed neutron stars are the strangeness-mixed ones, we find that the central densities increase.