Phase diagram of neutron-rich nuclear matter and its impact on astrophysics

TL;DR

This paper explores phase transitions in neutron-rich nuclear matter, focusing on the crust-core transition and hyperonic effects, with implications for supernovae and neutron star structure.

Contribution

It introduces a quasi-particle model to analyze the anomalous thermodynamics of the crust-core transition and examines hyperonic effects on the equation of state in neutron stars.

Findings

Long-range Coulomb interactions cause ensemble inequivalence and clusterized phases.

Hyperonic degrees of freedom significantly alter the neutron star equation of state.

A self-consistent mean-field approach characterizes phase transitions at high densities.

Abstract

Dense matter as it can be found in core-collapse supernovae and neutron stars is expected to exhibit different phase transitions which impact the matter composition and equation of state, with important consequences on the dynamics of core-collapse supernova explosion and on the structure of neutron stars. In this paper we will address the specific phenomenology of two of such transitions, namely the crust-core solid-liquid transition at sub-saturation density, and the possible strange transition at super-saturation density in the presence of hyperonic degrees of freedom. Concerning the neutron star crust-core phase transition at zero and finite temperature, it will be shown that, as a consequence of the presence of long-range Coulomb interactions, the equivalence of statistical ensembles is violated and a clusterized phase is expected which is not accessible in the grand-canonical ensemble. A specific quasi-particle model will be introduced to illustrate this anomalous thermodynamics and some quantitative results relevant for the supernova dynamics will be shown. The opening of hyperonic degrees of freedom at higher densities corresponding to the neutron stars core modifies the equation of state. The general characteristics and order of phase transitions in this regime will be analyzed in the framework of a self-consistent mean-field approach.