Formation of stars and planets: the role of magnetic fields |
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| Authors: | R Salmeron |
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| Institution: | (1) Institute for Theoretical Astrophysics at the Zentrum f?r Astronomie of the University Heidelberg, Albert-Ueberle-Str. 2, Heidlberg, Germany |
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| Abstract: | Star formation is thought to be triggered by gravitational collapse of the dense cores of molecular clouds. Angular momentum
conservation during the collapse results in the progressive increase of the centrifugal force, which eventually halts the
inflow of material and leads to the development of a central mass surrounded by a disc. In the presence of an angular momentum
transport mechanism, mass accretion onto the central object proceeds through this disc, and it is believed that this is how
stars typically gain most of their mass. However, the mechanisms responsible for this transport of angular momentum are not
well understood. Although the gravitational field of a companion star or even gravitational instabilities (particularly in
massive discs) may play a role, the most general mechanisms are turbulence viscosity driven by the magnetorotational instability (MRI), and outflows accelerated centrifugally from the surfaces of the disc. Both processes are powered by the action of magnetic fields and
are, in turn, likely to strongly affect the structure, dynamics, evolutionary path and planet-forming capabilities of their
host discs. The weak ionisation of protostellar discs, however, may prevent the magnetic field from effectively coupling to
the gas and shear and driving these processes. Here I examine the viability and properties of these magnetically-driven processes
in protostellar discs. The results indicate that, despite the weak ionisation, the magnetic field is able to couple to the
gas and shear for fluid conditions thought to be satisfied over a wide range of radii in these discs. |
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