Role of isospin physics in supernova matter and neutron stars

TL;DR

This paper explores the phase transition, composition, and structure of hot protoneutron stars and hyperon-rich neutron stars, emphasizing the roles of symmetry energy, neutrino trapping, and hyperons in their evolution and properties.

Contribution

It provides new insights into how symmetry energy, neutrino trapping, and hyperons influence the phase transition and structure of protoneutron stars within a relativistic mean-field framework.

Findings

Liquid-gas phase transition suppresses cluster yield and reduces neutron-proton asymmetry.

Symmetry energy has a modest effect on phase transition boundaries and critical temperature.

Neutrino trapping delays hyperon appearance and affects star composition.

Abstract

We investigate the liquid-gas phase transition of hot protoneutron stars shortly after their birth following supernova explosion and the composition and structure of hyperon-rich (proto)neutron stars within a relativistic mean-field model where the nuclear symmetry energy has been constrained from the measured neutron skin thickness of finite nuclei. Light clusters are abundantly formed with increasing temperature well inside the neutrino-sphere for an uniform supernova matter. Liquid-gas phase transition is found to suppress the cluster yield within the coexistence phase as well as decrease considerably the neutron-proton asymmetry over a wide density range. We find symmetry energy has a modest effect on the boundaries and the critical temperature for the liquid-gas phase transition, and the composition depends more sensitively on the number of trapped neutrinos and temperature of the protoneutron star. The influence of hyperons in the dense interior of stars makes the overall equation of state soft. However, neutrino trapping distinctly delays the appearance of hyperons due to abundance of electrons. We also find that a softer symmetry energy further makes the onset of hyperon less favorable. The resulting structures of the (proto)neutron stars with hyperons and with liquid-gas phase transition are discussed.