Multi-Fluid Simulation of the Magnetic Field Evolution in Neutron Stars

TL;DR

This paper uses numerical simulations to investigate how ambipolar and ohmic diffusion influence the long-term magnetic field evolution inside neutron stars, considering a multi-fluid plasma model.

Contribution

It introduces a multi-fluid simulation approach to study magnetic field evolution in neutron stars, accounting for complex interactions and diffusion processes.

Findings

Magnetic fields evolve through distinct quasi-equilibrium states.

Characteristic time scales for magnetic and density fluctuations are estimated.

The model captures the effects of weak interactions and fluid collisions.

Abstract

Using a numerical simulation, we study the effects of ambipolar diffusion and ohmic diffusion on the magnetic field evolution in the interior of an isolated neutron star. We are interested in the behavior of the magnetic field on a long time scale, over which all Alfven and sound waves have been damped. We model the stellar interior as an electrically neutral plasma composed of neutrons, protons and electrons, which can interact with each other through collisions and electromagnetic forces. Weak interactions convert neutrons and charged particles into each other, erasing chemical imbalances. As a first step, we assume that the magnetic field points in one fixed Cartesian direction but can vary along an orthogonal direction. We start with a uniform-density background threaded by a homogeneous magnetic field and study the evolution of a magnetic perturbation as well as the density fluctuations it induces in the particles. We show that the system evolves through different quasi-equilibrium states and estimate the characteristic time scales on which these quasi-equilibria occur.