Magnetic fields are known to play a crucial role in the star formation process, particularly in the formation of jets and outflows from protostellar discs. The magnetic field structure in star-forming regions is not always uniform and ordered, often containing regions of magnetic turbulence. We present grid-based, magneto-hydrodynamical simulations of the collapse of a one solar mass cloud core, to investigate the influence of complex magnetic field structures on outflow formation, morphology and efficiency. We compare three cases: a uniform field, a partially turbulent field and a fully turbulent field, with the same magnetic energy in all three cases. We find that collimated jets are produced in the uniform-field case, driven by a magneto-centrifugal mechanism. Outflows also form in the partially turbulent case, although weaker and less collimated, with an asymmetric morphology. The outflows launched from the partially turbulent case carry the same amount of mass as the uniform-field case but at lower speeds, having only have 71% of the momentum of the uniform-field case. In the case of a fully turbulent field, we find no significant outflows at all. Moreover, the turbulent magnetic field initially reduces the accretion rate and later induces fragmentation of the disc, forming multiple protostars. We conclude that a uniform poloidal component of the magnetic field is necessary for the driving of jets.
Star formation and jet launching in solar-type accretion discs, comparing three different initial magnetic field structures: uniform (left), partially turbulent (middle), and fully turbulent (right).
Corresponding simulation movie:
[ turb_b_jets.mp4, 57MB mpeg 4 video ]
We thank the anonymous referee for their valuable suggestions which helped us to improve this paper. IG would like to thank the Australian National University and the Research School and Astronomy and Astrophysics for the opportunity and funding provided as part of the Summer Research Scholarship program. RK thanks the Australian government for the Australian government research training program scholarship stipend. CF acknowledges funding provided by the Australian Research Council's Discovery Projects (grants DP150104329 and DP170100603), the Future Fellowship scheme (grant FT180100495), and the Australia-Germany Joint Research Cooperation Scheme (UA-DAAD). The simulations and data analyses presented in this work used high-performance-computing resources provided by the Leibniz Rechenzentrum and the Gauss Centre for Supercomputing (grants pr32lo, pr48pi and GCS Large-scale project 10391) and from the Australian National Computational Infrastructure (grant ek9, fu7) in the framework of the National Computational Merit Allocation Scheme and the ANU Allocation Scheme. The simulation software FLASH was in part developed by the DOE-supported Flash Centre for Computational Science at the University of Chicago. Visualisations were made using Visit (Childs et al. 2012). Analysis was performed using yt (Turk et al. 2011).