Magnetic fields in early protostellar disk formation

TL;DR

This paper uses 3D MHD simulations to demonstrate how turbulent magnetic reconnection facilitates protostellar disk formation by removing magnetic flux and preventing magnetic braking catastrophe, aligning with the Lazarian & Vishniac model.

Contribution

It provides the first detailed simulation-based analysis of turbulent reconnection effects on early protostellar disk formation, validating theoretical models.

Findings

Turbulent reconnection enables disk formation by removing magnetic flux.

Magnetic flux transport occurs outward via turbulence, reducing magnetic coupling.

Change in magnetic field topology from monopole to dipole aids disk formation.

Abstract

We consider formation of accretion disks from a realistically turbulent molecular gas using 3D MHD simulations. In particular, we analyze the effect of the fast turbulent reconnection described by the Lazarian & Vishniac (1999) model for the removal of magnetic flux from a disk. With our numerical simulations we demonstrate how the fast reconnection enables protostellar disk formation resolving the so-called "magnetic braking catastrophe". In particular, we provide a detailed study of the dynamics of a 0.5 M$_\odot$ protostar and the formation of its disk for up to several thousands years. We measure the evolution of the mass, angular momentum, magnetic field, and turbulence around the star. We consider effects of two processes that strongly affect the magnetic transfer of angular momentum, both of which are based on turbulent reconnection: the first, "reconnection diffusion", removes the magnetic flux from the disk, the other involves the change of the magnetic field's topology, but does not change the absolute value of the magnetic flux through the disk. We demonstrate that for the first mechanism, turbulence causes a magnetic flux transport outward from the inner disk to the ambient medium, thus decreasing the coupling of the disk to the ambient material. A similar effect is achieved through the change of the magnetic field's topology from a split monopole configuration to a dipole configuration. We explore how both mechanisms prevent the catastrophic loss of disk angular momentum and compare both above turbulent reconnection mechanisms with alternative mechanisms from the literature.