Empirical constraints on the high-density equation of state from multi-messenger observables

TL;DR

This paper investigates correlations between neutron star observables and high-density nuclear matter properties, using model-independent equations of state to improve constraints on the nuclear equation of state from multi-messenger astrophysical data.

Contribution

It introduces a method to derive model-independent correlations between neutron star observables and nuclear matter properties, aiding in constraining the high-density equation of state.

Findings

Neutron star tidal deformability and radius strongly correlate with pressure, energy density, and sound velocity at various densities.

Model-independent correlations are consistent with mean-field nuclear models.

Precise radius measurements can significantly improve understanding of matter at twice nuclear saturation density.

Abstract

We search for possible correlations between neutron star observables and thermodynamic quantities that characterize high density nuclear matter. We generate a set of model-independent equations of state describing stellar matter from a Taylor expansion around saturation density. Each equation of state which is a functional of the nuclear matter parameters is thermodynamically consistent, causal and compatible with astrophysical observations. We find that the neutron star tidal deformability and radius are strongly correlated with the pressure, the energy density and the sound velocity at different densities. Similar correlations are also exhibited by a large set of mean-field models based on non-relativistic and relativistic nuclear energy density functionals. These model independent correlations can be employed to constrain the equation of state at different densities above saturation from measurements of NS properties with multi-messenger observations. In particular, precise constraints on the radius of PSR J0030+0451 thanks to NICER observations would allow to better infer the properties of matter around two times the nuclear saturation density.