Strong magnetic fields and pasta phases revisited

TL;DR

This paper investigates the structure and composition of neutron star crusts under strong magnetic fields, using a detailed liquid drop model and relativistic mean-field theories to improve understanding of crust-core transitions in magnetars.

Contribution

It introduces a refined model for neutron star crusts considering magnetic fields and symmetry energy effects, improving accuracy over previous approximate methods.

Findings

Magnetic fields extend the inhomogeneous crust region in neutron stars.

The symmetry energy slope influences crustal inhomogeneity extent.

The model provides more precise crust-core transition estimates.

Abstract

In this work, we compute the structure and composition of the inner crust of a neutron star in the presence of a strong magnetic field, such as it can be found in magnetars. To determine the geometry and characteristics of the crust inhomogeneities, we consider the compressible liquid drop model, where surface and Coulomb terms are included in the variational equations, and we compare our results with previous calculations based on more approximate treatments. For the equation of state (EoS), we consider two non-linear relativistic mean-field models with different slopes of the symmetry energy, and we show that the extension of the inhomogeneous region inside the star core due to the magnetic field strongly depends on the behavior of the symmetry energy in the crustal EoS. Finally, we argue that the extended spinodal instability observed in previous calculations can be related to the presence of small amplitude density fluctuations in the magnetar outer core, rather than to a thicker solid crust. The compressible liquid drop model formalism, while in overall agreement with the previous calculations, leads to a systematic suppression of the metastable solutions, thus allowing a more precise estimation of the crust-core transition density and pressure, and therefore a better estimation of the crustal radius.