Collapse, outflows and fragmentation of massive, turbulent and magnetized prestellar barotropic 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 Max Planck Institute for Astronomy, Königsthul 17, 69117 Heidelberg, Germany
³ Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
⁴ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
⁵ Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
⁶ Laboratoire AIM, Paris-Saclay, CEA/IRFU/SAp - CNRS - Université Paris Diderot, 91191 Gif-sur-Yvette Cedex, France
⁷ Institute for theoretical Physics, University of Zürich, 8057 Zürich, Switzerland

Received: 3 November 2010
Accepted: 28 December 2010

Abstract

Context. Stars, and more particularly massive stars, have a drastic impact on galaxy evolution. Yet the conditions in which they form and collapse are still not fully understood.

Aims. In particular, the influence of the magnetic field on the collapse of massive clumps is relatively unexplored, it is therefore of great relevance in the context of the formation of massive stars to investigate its impact.

Methods. We perform high resolution, MHD simulations of the collapse of one hundred solar masses, turbulent and magnetized clouds, with the adaptive mesh refinement code RAMSES. We compute various quantities such as mass distribution, magnetic field, and angular momentum within the collapsing core and study the episodic outflows and the fragmentation that occurs during the collapse.

Results. The magnetic field has a drastic impact on the cloud evolution. We find that magnetic braking is able to substantially reduce the angular momentum in the inner part of the collapsing cloud. Fast and episodic outflows are being launched with typical velocities of the order of 1−3 km s^-1, although the highest velocities can be as high as 20−40 km s^-1. The fragmentation in several objects is reduced in substantially magnetized clouds with respect to hydrodynamical ones by a factor of the order of 1.5−2.

Conclusions. We conclude that magnetic fields have a significant impact on the evolution of massive clumps. In combination with radiation, magnetic fields largely determine the outcome of massive core collapse. We stress that numerical convergence of MHD collapse is a challenging issue. In particular, numerical diffusion appears to be important at high density and therefore could possibly lead to an overestimation of the number of fragments.