Magnetic Diffusion in Star Formation

TL;DR

This paper investigates how magnetic diffusion influences star formation across different scales, highlighting the roles of magnetic field gradients, nonlinear flows, and diffusion processes in enabling protostellar disk formation.

Contribution

It provides a detailed analysis of magnetic diffusion mechanisms from cloud to star-disk scales, emphasizing their impact on magnetic flux loss and disk formation.

Findings

Magnetic diffusion is enhanced by strong magnetic field gradients.

Rapid diffusion near protostars facilitates disk formation.

Magnetic flux loss prevents magnetic braking catastrophe.

Abstract

Magnetic diffusion plays a vital role in star formation. We trace its influence from interstellar cloud scales down to star-disk scales. On both scales, we find that magnetic diffusion can be significantly enhanced by the buildup of strong gradients in magnetic field structure. Large scale nonlinear flows can create compressed cloud layers within which ambipolar diffusion occurs rapidly. However, in the flux-freezing limit that may be applicable to photoionized molecular cloud envelopes, supersonic motions can persist for long times if driven by an externally generated magnetic field that corresponds to a subcritical mass-to-flux ratio. In the case of protostellar accretion, rapid magnetic diffusion (through Ohmic dissipation with additional support from ambipolar diffusion) near the protostar causes dramatic magnetic flux loss. By doing so, it also allows the formation of a centrifugal disk, thereby avoiding the magnetic braking catastrophe.