Strong correlations of neutron star radii with the slopes of nuclear matter incompressibility and symmetry energy at saturation

TL;DR

This study reveals a strong correlation between neutron star radii and the slopes of nuclear matter incompressibility and symmetry energy, using various models to connect nuclear physics parameters with astrophysical observations.

Contribution

It demonstrates that neutron star radii are strongly correlated with specific nuclear matter parameters, independent of star mass, providing a new link between nuclear physics and astrophysics.

Findings

Neutron star radii correlate with slopes of nuclear matter parameters.

Correlation is nearly independent of neutron star mass.

Estimated radii for 1.4 solar mass stars range from 11.09 to 12.86 km.

Abstract

We examine the correlations of neutron star radii with the nuclear matter incompressibility, symmetry energy, and their slopes, which are the key parameters of the equation of state (EoS) of asymmetric nuclear matter. The neutron star radii and the EoS parameters are evaluated using a representative set of 24 Skyrme-type effective forces and 18 relativistic mean field models, and two microscopic calculations, all describing 2$M_\odot$ neutron stars. Unified EoSs for the inner-crust-core region have been built for all the phenomenological models, both relativistic and non-relativistic. Our investigation shows the existence of a strong correlation of the neutron star radii with the linear combination of the slopes of the nuclear matter incompressibility and the symmetry energy coefficients at the saturation density. Such correlations are found to be almost independent of the neutron star mass in the range $0.6\text{-}1.8M_{\odot}$. This correlation can be linked to the empirical relation existing between the star radius and the pressure at a nucleonic density between one and two times saturation density, and the dependence of the pressure on the nuclear matter incompressibility, its slope and the symmetry energy slope. The slopes of the nuclear matter incompressibility and the symmetry energy coefficients as estimated from the finite nuclei data yield the radius of a $1.4M_{\odot}$ neutron star in the range $11.09\text{-}12.86$ km.