Magnetic Field Diffusion and the Formation of Circumstellar Disks

TL;DR

This study uses non-ideal MHD simulations with detailed chemistry to show that circumstellar disks can form early in star formation due to magnetic field diffusion reducing magnetic braking.

Contribution

It demonstrates that magnetic field diffusion in non-ideal MHD models allows early disk formation, challenging previous notions of catastrophic magnetic braking.

Findings

Centrifugal disks form in early star formation stages.

Magnetic diffusion reduces magnetic braking.

Realistic non-ideal MHD prevents catastrophic braking.

Abstract

A non-ideal MHD collapse calculation employing the axisymmetric thin-disk approximation is used to resolve cloud core collapse down to the scales of the second (stellar) core. Rotation and a magnetic braking torque are included in the model, and the partial ionization resulting in ambipolar diffusion and Ohmic dissipation is calculated from a detailed chemical network. We find that a centrifugal disk can indeed form in the earliest stage of star formation, due to a shut-off of magnetic braking caused by magnetic field diffusion in the first core region. Thus, there is no catastrophic magnetic braking in a model with realistic non-ideal MHD.