On the role of magnetic fields in star formation

TL;DR

This paper questions the role of magnetic fields in star formation, arguing that current simulations including magnetic effects may not accurately represent the physical processes due to unrealistic parameters, and that regions forming stars might be effectively free of magnetic influence.

Contribution

It challenges the assumption that magnetic fields are crucial in star formation by highlighting limitations of current magnetohydrodynamic simulations and proposing that magnetic dissipation may reduce magnetic influence.

Findings

Simulations with magnetic fields may not capture true physics due to high magnetic Prandtl number effects.

Regions forming stars might be nearly free of magnetic fields due to reconnection and dissipation.

Ignoring magnetic fields in certain scales might produce more realistic results than including them with unrealistic parameters.

Abstract

Magnetic fields are observed in star forming regions. However simulations of the late stages of star formation that do not include magnetic fields provide a good fit to the properties of young stars including the initial mass function (IMF) and the multiplicity. We argue here that the simulations that do include magnetic fields are unable to capture the correct physics, in particular the high value of the magnetic Prandtl number, and the low value of the magnetic diffusivity. The artificially high (numerical and uncontrolled) magnetic diffusivity leads to a large magnetic flux pervading the star forming region. We argue further that in reality the dynamics of high magnetic Prandtl number turbulence may lead to local regions of magnetic energy dissipation through reconnection, meaning that the regions of molecular clouds which are forming stars might be essentially free of magnetic fields. Thus the simulations that ignore magnetic fields on the scales on which the properties of stellar masses, stellar multiplicities and planet-forming discs are determined, may be closer to reality than those which include magnetic fields, but can only do so in an unrealistic parameter regime.