# On the self-consistent general relativistic equilibrium equations of neutron stars

## TL;DR

This paper develops a self-consistent relativistic model for neutron stars that enforces global charge neutrality, revealing new equilibrium configurations with complex electrodynamical structures and overcritical electric fields at the core-crust boundary.

## Contribution

It introduces a novel approach solving Einstein-Maxwell and Thomas-Fermi equations simultaneously for neutron stars with global neutrality, expanding the understanding of their equilibrium states.

## Key findings

- Existence of a new family of globally neutral neutron star configurations.
- Electrodynamical structure characterized by a thin shell with overcritical electric fields.
- Configurations depend on the Fermi energy at the core surface.

## Abstract

We address the existence of globally neutral neutron star configurations in contrast with the traditional ones constructed by imposing local neutrality. The equilibrium equations describing this system are the Einstein-Maxwell equations which must be solved self-consistently with the general relativistic Thomas-Fermi equation and $\beta$-equilibrium condition. To illustrate the application of this novel approach we adopt the Baym, Bethe, and Pethick (1971) strong interaction model of the baryonic matter in the core and of the white-dwarf-like material of the crust. We illustrate the crucial role played by the boundary conditions satisfied by the leptonic component of the matter at the interface between the core and the crust. For every central density an entire new family of equilibrium configurations exists for selected values of the Fermi energy of the electrons at the surface of the core. Each such configuration fulfills global charge neutrality and is characterized by a non-trivial electrodynamical structure. The electric field extends over a thin shell of thickness $\sim \hbar/(m_e c)$ between the core and the crust and becomes largely overcritical in the limit of decreasing values of the crust mass.