General Relativistic Mean-field Dynamo Model for Proto-neutron Stars

TL;DR

This paper presents the first numerical simulations of magnetic field growth in proto-neutron stars using non-ideal general relativistic magnetohydrodynamics, demonstrating how mean-field dynamo processes can amplify magnetic fields to observed levels.

Contribution

It introduces a novel GRMHD simulation approach to model mean-field dynamo effects in proto-neutron stars, exploring the impact of turbulence and initial conditions on magnetic field amplification.

Findings

Dynamo process can exponentially amplify magnetic fields to observed strengths.

Growth rates depend linearly on the dynamo coefficient.

Initial magnetic field configuration influences the growth period and rate.

Abstract

Neutron stars, and magnetars in particular, are known to host the strongest magnetic fields in the Universe. The origin of these strong fields is a matter of controversy. In this preliminary work, via numerical simulations, we study, for the first time in non-ideal general relativistic magnetohydrodynamic (GRMHD) regime, the growth of the magnetic field due to the action of the mean-field dynamo due to sub-scale, unresolved turbulence. The dynamo process, combined with the differential rotation of the (proto-)star, is able to produce an exponential growth of any initial magnetic seed field up to the values required to explain the observations. By varying the dynamo coefficient we obtain different growth rates. We find a quasi-linear dependence of the growth rates on the intensity of the dynamo. Furthermore, the time interval in which exponential growth occurs and the growth rates also seems to depend on the initial configuration of the magnetic field.