Protostars and Planets VI, Heidelberg, July 15-20, 2013
The Early Era: How do protostellar discs form?
Joos, Marc (Service d\'Astrophysique, CEA - Laboratoire de Radioastronomie, ENS, LERMA, Observatoire de Paris, Université Pierre et Marie Curie)
Hennebelle, Patrick (Service d\'Astrophysique, CEA - Laboratoire de Radioastronomie, ENS, LERMA, Observatoire de Paris, Université Pierre et Marie Curie)
Ciardi, Andrea (Laboratoire de Radioastronomie, ENS, LERMA, Observatoire de Paris, Université Pierre et Marie Curie)
Fromang, Sebastien (Service d\'Astrophysique, CEA)
The understanding of disks formation and their early stages evolution is crucial to understand planets formation. Prestellar collapse leads to the formation of a protostar as well as the possible build-up of a disk. However, most previous studies, limited to cases where the magnetic field and the rotation axis of the cloud are aligned, have found that even a relatively weak magnetic field may prevent the early formation of massive disks and their fragmentation. Moreover, very few studies investigated the combined effects of magnetic field and turbulence.
We perform three-dimensional, adaptive mesh, numerical simulations of magnetically supercritical collapsing dense cores in both non-turbulent and turbulent environment, using the magneto-hydrodynamic code Ramses.
At variance with earlier analyses, we show that the transport of angular momentum acts less efficiently in collapsing cores with non-aligned rotation and magnetic field. We also show that the turbulence is responsible for a misalignment between the rotation axis and the magnetic field and can diffuse out the magnetic field of the inner regions efficiently. The magnetic braking is therefore reduced, and massive disks can be built. If the disks are massive enough and the magnetization not too strong, fragmentation can occur.
The early formation of massive disks and their fragmentation can take place at moderate magnetic intensities if the rotation axis is tilted or in a turbulent environment, because of misalignment and turbulent diffusion.
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