# Anisotropic crystal structure of magnetized neutron star crust

## TL;DR

This paper investigates how strong magnetic fields cause anisotropic deformation in neutron star crust crystals, potentially triggering magnetar activity and leading to a transition to liquid crystal states under extreme conditions.

## Contribution

It reveals that magnetic fields induce anisotropic pressure and deformation in neutron star crust crystals, identifying instability limits and proposing a transition to liquid crystal phases.

## Key findings

- Magnetic fields cause anisotropic stretching or shrinking of crust crystals.
- Phonon mode instability limits magnetic field variation without destroying the crystal.
- Extreme pressure anisotropy may lead to a liquid crystal phase.

## Abstract

Although crystallized neutron star crust is responsible for many fascinating observational phenomena, its actual microscopic structure in tremendous gravitational and magnetic fields is not understood. Here we show that in a non-uniform magnetic field, three-dimensional ionic Coulomb crystals comprising the crust may stretch or shrink while their electrostatic pressure becomes anisotropic. The pressure depends non-linearly on the magnitude of the stretch, so that a continuous magnetic field evolution may result in an abrupt crystal elongation or contraction. This may provide a trigger for magnetar activity. A phonon mode instability is revealed, which sets the limits of magnetic field variation beyond which the crystal is destroyed. These limits sometimes correspond to surprisingly large deformations. It is not known what happens to crust matter subject to a pressure anisotropy exceeding these limits. We hypothesize that the ion system then possesses a long-range order only in one or two dimensions, that is becomes a liquid crystal.