The Early Era: How do protostellar discs form?

Abstract

Discs are a key element in star and planet formation; however, magnetic fields can efficiently transport angular momentum away from the central region of the collapsing core during the dense core collapse, preventing disc formation. We perform numerical simulations of magnetically supercritical collapsing cores with a misalignment between the rotation axis and the magnetic field (Joos et al. 2012) and in a turbulent environment (Joos et al. 2013). The early formation of massive discs can take place at moderate magnetic intensities if the rotation axis is tilted or in a turbulent environment, because of misalignment and turbulent diffusion.

Turbulence-induced disc formation in strongly magnetized cloud cores

“…We again emphasise that we did not find any qualitative differences for different realisations of the turbulence field. We therefore believe that also in the runs with lower and higher masses a change in the turbulence field would not significantly alter the results (see also Joos et al 2013).…”

“…From the work on disc formation under the influence of magnetic fields done so far a common picture seems to arise: Due to the turbulent nature of star forming regions the classical picture of a well-ordered magnetic field structure and coherent rotational motions, used by Mouschovias & Paleologou (1980) to assess the efficiency of magnetic braking, seems to break down. Under realistic conditions a disordered and/or misaligned magnetic field structure (see also Hennebelle & Ciardi 2009;Ciardi & Hennebelle 2010;Joos et al 2012Joos et al , 2013 as well as turbulent shear flows emerge, which cause the classical magnetic braking efficiency to drop and allow for the formation of Keplerian discs in essentially all cases considered here. The likelihood of disc formation in the turbulent case is therefore higher than that for purely misaligned fields in non-turbulent cores (Krumholz et al 2013;Li et al 2013).…”

Simulated observations of young gravitationally unstable protoplanetary discs

“…Currently few observations constrain the formation and early evolution of protoplanetary discs around solar-type and low-mass protostars, despite the fast growing list of theoretical models on the dynamical evolution of star forming dense cores (e. g. Krasnopolsky, Li & Shang 2011;Machida, Inutsuka & Matsumoto 2011;Braiding & Wardle 2012;Joos et al 2013). The reason for this is that young protostars are surrounded by thick envelopes and power energetic outflows.…”