Letter to the Editor

Disk formation during collapse of magnetized protostellar cores^*

¹ Laboratoire de radioastronomie, UMR 8112 du CNRS, École normale supérieure et Observatoire de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France e-mail: patrick.hennebelle@ens.fr
² Laboratoire de Physique des Plasmas, UMR 7648 du CNRS, 10-12 Avenue de l'Europe, 78140 Velizy, France

Received: 29 July 2009
Accepted: 14 September 2009

Abstract

Context. In the context of star and planet formation, understanding the formation of disks is of fundamental importance.

Aims. Previous studies found that the magnetic field has a very strong impact on the collapse of a prestellar cloud, by possibly suppressing the formation of a disk even for relatively modest values of the magnetic intensity. Since observations infer that cores have a substantial level of magnetization, this raises the question of how disks form. However, most studies have been restricted to the case in which the initial angle, α, between the magnetic field and the rotation axis equals 0°. Here we explore and analyse the influence of non aligned configurations on disk formation.

Methods. We perform 3D ideal MHD, AMR numerical simulations for various values of μ, the ratio of the mass-to-flux to the critical mass-to-flux, and various values of α.

Results. We find that disks form more easily as α increases from 0 to 90°. We propose that as the magnetized pseudo-disks become thicker with increasing α, the magnetic braking efficiency is lowered. We also find that even small values of α (10–20°) show significant differences with the aligned case.

Conclusions. Within the framework of ideal MHD, and for our choice of initial conditions, centrifugally supported disks cannot form for values of μ smaller than 3 when the magnetic field and the rotation axis are perpendicular, and smaller than about 5–10 when they are perfectly aligned.