Pasta phases in neutron stars under strong magnetic fields

TL;DR

This study investigates how strong magnetic fields influence the structure and composition of neutron star crusts, revealing extended crust regions, diverse pasta shapes, and increased proton fractions.

Contribution

It introduces a relativistic mean-field model analysis of pasta phases in neutron star crusts under strong magnetic fields, including anomalous magnetic moments and various geometries.

Findings

Strong magnetic fields extend the neutron star crust.

Multiple pasta geometries occur at certain magnetic field strengths.

Magnetic fields increase proton fractions in the crust.

Abstract

In the present work, we consider nuclear matter in the innermost crust of neutron stars under the presence of a strong magnetic field within the framework of a relativistic mean-field description. Two models with a different slope of the symmetry energy are considered in order to discuss the density-dependence of the equation of state on the crust structure. The non-homogeneous matter in $\beta$-equilibrium is described within the coexisting phases method, and the effect of including the anomalous magnetic moment is discussed. Five different geometries for the pasta structures are considered. It is shown that strong magnetic fields cause an extension of the inner crust of the neutron stars, with the occurrence of a series of disconnected non-homogeneous matter regions above the one existing for a null magnetic field. Moreover, we observed that in these disconnected regions, for some values of the magnetic field, all five different cluster geometrical shapes occur, and the gas density is close to the cluster density. Also, the pressure at the neutron star crust-core transition much larger than the pressure obtained for a zero magnetic field. Another noticeable effect of the presence of strong magnetic fields is the increase of the proton fraction, favoring the appearance of protons in the gas background.