Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...459..371r&link_type=abstract
Astrophysical Journal v.459, p.371
Astronomy and Astrophysics
Astronomy
6
Accretion, Accretion Disks, Instabilities, Magnetohydrodynamics: Mhd
Scientific paper
We follow the evolution of a closed loop of relatively weak poloidal magnetic field, originally embedded somewhat above the midplane in a hydrostatic accretion disk. The equations of magnetohydrodynamics are solved on a numerical grid in axisymmetric geometry. Viscous heating, radiative transfer, and the horizontal and vertical components of the gravity of the central star are taken into account. As the evolution proceeds, toroidal field is built up as a result of shear in the disk, and the field becomes buoyant as a result of interchange modes of the Parker instability. The effective wavelength of the buoyant instability, and its dependence on the strength of the initial field loop, are found to be consistent with a linear stability analysis. The buoyancy results in turbulent motions and expulsion of some field from the disk. Eventually, a saturation state is reached, in which the field assumes a patchy structure, and the ratio of gas to magnetic pressure stabilizes in the range 1-5. Outward angular momentum transfer and an accompanying radial expansion of the magnetized region occur as a result of magnetic torques, and an equivalent α-viscosity parameter is estimated. The implications of these results on the generation of a magnetic dynamo in a disk are discussed.
Bodenheimer Peter
Lin Doug N. C.
Rozyczka Michal
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