The neutron star inner crust: an empirical essay

TL;DR

This paper investigates how the inner crust's properties influence neutron star mass-radius relations, using empirical equations of state and analyzing the impact on the star's radius, with implications for gravitational wave observations.

Contribution

It introduces empirical equations of state for the neutron star inner crust and examines their effects on the star's radius and speed of sound, providing new insights into neutron star structure.

Findings

Different speed of sound behaviors can alter the star's radius by over 1.1 km.

The inner crust's contribution significantly impacts the mass-radius relation.

Results relate to constraints from GW170817 observations.

Abstract

In this work we study how the small contribution of the inner crust to the total equation of state (EoS) of a neutron star affects its mass-radius relation, focusing on the canonical mass of 1.4$M_\odot$. We build empirical EoS of the kind - $p = K\epsilon^{\gamma} + b$ - in the range of 0.003 fm$^{-3}~<~n~<~$0.08 fm$^{-3}$ and also calculate the speed of sound in this region. We see that different behaviours of the speed of sound can affect the radius of the canonical star by more than 1.1 km. This result can help us understand extreme results as GW170817, where some studies indicate that the radius of the canonical star cannot exceed 11.9 km.