Towards a metallurgy of neutron star crusts

TL;DR

This paper proposes that the inner crust of neutron stars has a complex, ferroelectric-like structure due to neutron-induced interactions, challenging the traditional simple lattice model and affecting observable star properties.

Contribution

It introduces a new model for neutron star crusts where interstitial neutrons induce ferroelectric-like structures, expanding understanding beyond the standard lattice assumption.

Findings

Neutrons cause an attractive interaction between nuclei at high densities.

The inner crust likely forms a ferroelectric-like structure similar to BaTiO$_3$.

Implications for neutron star observables are discussed.

Abstract

In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic (bcc) lattice of nuclei immersed in an essentially uniform electron gas. We show that at densities above that for neutron drip ($\sim4\times10^11$) g cm$^{-3}$ or roughly one thousandth of nuclear matter density, the interstitial neutrons give rise to an attractive interaction between nuclei that renders the lattice unstable. We argue that the likely equilibrium structure is similar to that in displacive ferroelectric materials such as BaTiO$_3$. As a consequence, properties of matter in the inner crust are expected to be much richer than previously appreciated and we mention consequences for observable neutron star properties.