A Nuclear Equation of State Inferred from Stellar r-process Abundances

TL;DR

This paper infers a neutron star equation of state by linking stellar r-process abundances to neutron star merger models, providing constraints consistent with current observational bounds.

Contribution

It introduces a phenomenological EOS derived from r-process element abundances in metal-poor stars, connecting stellar observations with neutron star physics.

Findings

Derived EOS parameters consistent with current constraints

Estimated neutron star radius of approximately 12.25 km

Predicted maximum neutron star mass around 2.17 solar masses

Abstract

Binary neutron star mergers (NSMs) have been confirmed as one source of the heaviest observable elements made by the rapid neutron-capture (r-) process. However, modeling NSM outflows -- from the total ejecta masses to their elemental yields -- depends on the unknown nuclear equation of state (EOS) that governs neutron-star structure. In this work, we derive a phenomenological EOS by assuming that NSMs are the dominant sources of the heavy element material in metal-poor stars with r-process abundance patterns. We start with a population synthesis model to obtain a population of merging neutron star binaries and calculate their EOS-dependent elemental yields. Under the assumption that these mergers were responsible for the majority of r-process elements in the metal-poor stars, we find parameters representing the EOS for which the theoretical NSM yields reproduce the derived abundances from observations of metal-poor stars. For our proof-of-concept assumptions, we find an EOS that is slightly softer than, but still in agreement with, current constraints, e.g., by the Neutron Star Interior Composition Explorer, with $R_{1.4}=12.25\pm 0.03$~km and $M_{\textrm TOV}$ of $2.17\pm 0.03$~M$_\odot$(statistical uncertainties, neglecting modeling systematics).