Astrophysical Implications on Hyperon Couplings and Hyperon Star Properties with Relativistic Equations of States

Abstract

Hyperons are essential constituents in the neutron star interior. The poorly known hyperonic interaction is a source of uncertainty for studying laboratory hypernuclei and neutron star observations. In this work, we perform Bayesian inference of phenomenological hyperon–nucleon interactions using the tidal deformability measurement of the GW170817 binary neutron star merger as detected by LIGO/Virgo and the mass–radius measurements of PSR J0030+0541 and PSR J0740+6620 as detected by NICER. The analysis is based on a set of stiff relativistic neutron star matter equation of states with hyperons from the relativistic mean-field theory, naturally fulfilling the causality requirement and empirical nuclear matter properties. We specifically utilize the strong correlation recently deduced between the scalar and vector meson–hyperon couplings, imposed by the measured Λ separation energy in single-Λ hypernuclei, and perform four different tests with or without the strong correlation. We find that the laboratory hypernuclear constraint ensures a large enough Λ–scalar–meson coupling to match the large vector coupling in hyperon star matter. When adopting the current most probable intervals of hyperon couplings from the joint analysis of laboratory and astrophysical data, we find the maximum mass of hyperon stars is at most ${2.176}_{-0.202}^{+0.085}{M}_{\odot }$ (68% credible interval) from the chosen set of stiff equation of states. The reduction of the stellar radius due to hyperons is quantified based on our analysis and various hyperon star properties are provided.

Keywords

• Neutron star cores
• Neutron stars
• Gravitational waves
• Pulsars