Disc formation in turbulent massive cores: Circumventing the magnetic braking catastrophe

TL;DR

This study uses simulations to show that turbulence in massive star-forming cores naturally enables the formation of Keplerian discs by disrupting magnetic braking, challenging previous non-turbulent models.

Contribution

It demonstrates that turbulence, not magnetic flux loss or misalignment, facilitates Keplerian disc formation in massive cores, addressing the magnetic braking catastrophe.

Findings

Turbulence leads to the formation of Keplerian discs up to 100 AU.

Magnetic flux loss and misalignment are not primary factors in disc formation.

Turbulent surroundings carry angular momentum via local shear flows.

Abstract

We present collapse simulations of 100 M_{\sun}, turbulent cloud cores threaded by a strong magnetic field. During the initial collapse phase filaments are generated which fragment quickly and form several protostars. Around these protostars Keplerian discs with typical sizes of up to 100 AU build up in contrast to previous simulations neglecting turbulence. We examine three mechanisms potentially responsible for lowering the magnetic braking efficiency and therefore allowing for the formation of Keplerian discs. Analysing the condensations in which the discs form, we show that the build-up of Keplerian discs is neither caused by magnetic flux loss due to turbulent reconnection nor by the misalignment of the magnetic field and the angular momentum. It is rather a consequence of the turbulent surroundings of the disc which exhibit no coherent rotation structure while strong local shear flows carry large amounts of angular momentum. We suggest that the "magnetic braking catastrophe", i.e. the formation of sub-Keplerian discs only, is an artefact of the idealised non-turbulent initial conditions and that turbulence provides a natural mechanism to circumvent this problem.