Locating the inner edge of neutron star crust using terrestrial nuclear laboratory data

TL;DR

This study uses terrestrial nuclear data to precisely determine the neutron star crust's inner edge, revealing new constraints on the transition density and pressure, and implications for pulsar radius estimates.

Contribution

It introduces a method combining dynamical and thermodynamical approaches with recent nuclear data to accurately locate the neutron star crust's inner edge.

Findings

Transition density: 0.040-0.065 fm$^{-3}$

Transition pressure: 0.01-0.26 MeV/fm$^{3}$

New radius limits for Vela pulsar

Abstract

Within both dynamical and thermodynamical approaches using the equation of state for neutron-rich nuclear matter constrained by the recent isospin diffusion data from heavy-ion reactions in the same sub-saturation density range as the neutron star crust, the density and pressure at the inner edge separating the liquid core from the solid crust of neutron stars are determined to be 0.040 fm$^{-3}$ $\leq \rho_{t}\leq 0.065$ fm$^{-3}$ and 0.01 MeV/fm$^{3}$ $\leq P_{t}\leq 0.26$ MeV/fm$^{3}$, respectively. These together with the observed minimum crustal fraction of the total moment of inertia allow us to set a new limit for the radius of the Vela pulsar significantly different from the previous estimate. It is further shown that the widely used parabolic approximation to the equation of state of asymmetric nuclear matter leads systematically to significantly higher core-crust transition densities and pressures, especially with stiffer symmetry energy functionals.