Turbulence-induced disc formation in strongly magnetised cloud cores

TL;DR

This study uses simulations to show that Keplerian discs form early in strongly magnetised, turbulent cloud cores regardless of core mass or initial rotation, mainly due to magnetic field disorder and turbulence.

Contribution

It demonstrates that magnetic flux loss is not necessary for disc formation, highlighting the roles of magnetic field structure and turbulence in early Keplerian disc development.

Findings

Discs form within a few kyr after protostar formation.

Discs are 50-150 AU in size with masses of 0.05-0.1 M_sun.

Magnetic flux loss is not the main factor in disc formation.

Abstract

We present collapse simulations of strongly magnetised, turbulent molecular cloud cores with masses ranging from 2.6 to 1000 M_sun in order to study the influence of the initial conditions on the turbulence-induced disc formation mechanism proposed recently by Seifried et al. 2012. We find that Keplerian discs are formed in all cases independently of the core mass, the strength of turbulence, or the presence of global rotation. The discs appear within a few kyr after the formation of the protostar, are 50 - 150 AU in size, and have masses between 0.05 and a few 0.1 M_sun. During the formation of the discs the mass-to-flux ratio stays well below the critical value of 10 for Keplerian disc formation. Hence, flux-loss alone cannot explain the formation of Keplerian discs. The formation of rotationally supported discs at such early phases is rather due to the disordered magnetic field structure and due to turbulent motions in the surroundings of the discs, two effects lowering the classical magnetic braking efficiency. Binary systems occurring in the discs are mainly formed via the disc capturing mechanism rather than via disc fragmentation, which is largely suppressed by the presence of magnetic fields.