The Equation of State for the Nucleonic and Hyperonic Core of Neutron Stars

TL;DR

This paper refines models of neutron star cores to match recent observational constraints, analyzing how hyperon-nucleon interactions influence star properties and providing updated equations of state and mass-radius data.

Contribution

It introduces improved FSU2R and FSU2H models that satisfy observational and experimental constraints, enhancing understanding of hyperonic effects in neutron star cores.

Findings

Maximum neutron star mass is robust against hyperon-nucleon uncertainties.

Hyperon appearance depends strongly on hyperon-nuclear interaction uncertainties.

Updated models produce consistent mass-radius relations with recent observations.

Abstract

We reexamine the equation of state for the nucleonic and hyperonic inner core of neutron stars that satisfies the 2$M_{\odot}$ observations as well as the recent determinations of stellar radii below 13 km, while fulfilling the saturation properties of nuclear matter and finite nuclei together with the constraints on the high-density nuclear pressure coming from heavy-ion collisions. The recent nucleonic FSU2R and hyperonic FSU2H models are fine tuned improving the density dependence of pure neutron matter at subsaturation densities. The corresponding nuclear matter properties at saturation, the symmetry energy and its slope turn out to be compatible with recent experimental and theoretical determinations. We obtain the mass, radius and composition of neutron stars for the two updated models and study the impact on these properties of the uncertainties in the hyperon-nucleon couplings estimated from hypernuclear data. We find that the onset of appearance of each hyperon strongly depends on the hyperon-nuclear uncertainties, whereas the maximum masses for neutron stars differ by at most 0.1 $M_{\odot}$, although a larger deviation should be expected tied to the lack of knowledge of the hyperon potentials at the high densities present in the center of $2 M_\odot$ stars. For easier use, we provide tables with the results from the FSU2R and FSU2H models for the equation of state and the neutron star mass-radius relation.