A three-parameter characterization of neutron stars' mass-radius relation and equation of state

TL;DR

This paper introduces a three-parameter universal framework for describing neutron star mass-radius relations and equations of state, simplifying the inference of dense matter physics from observational data.

Contribution

It proposes a novel three-parameter universal description of neutron star properties applicable across various EoS models, enabling easier EoS inference from observations.

Findings

Universal relations accurately describe diverse EoS models.

New constraints on high-density neutron star matter.

Semi-analytic mapping simplifies EoS inference.

Abstract

Numerous models of neutron star (NS) equation of state (EoS) exist based on different superdense-matter physics approaches. Nevertheless, some NS properties show universal (EoS-independent) relations. Here, we propose a novel class of such universalities. Despite different physics inputs, a wide class of realistic nucleonic, hyperonic, and hybrid EoS models can be accurately described using only three parameters. For a given EoS, these are the mass and radius of the maximum-mass NS (or pressure and density in its center) and the radius of a half-maximum-mass star. With such a parametrization, we build universal analytic expressions for mass-radius and pressure-density relations. They form a semi-analytic mapping from the mass-radius relation to the EoS in NS cores (the so-called inverse Oppenheimer-Volkoff mapping). This mapping simplifies the process of inferring the EoS from observations of NS masses and radii. Applying it to current NS observations we set new limits on the high-density end of the EoS.