AAS 197, January 2001
Session 6. Planetary Nebulae: Young and Old
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

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[6.09] Structure Formation through Magnetohydrodynamical Instabilities in Protoplanetary Disks

K. Noguchi (IFS, Dept. of Physics, Univ. of Texas, Austin), T. Tajima (IFS, Dept. of Physics, Univ. of Texas, Austin, LANL), W. Horton (IFS, Dept. of Physics, Univ. of Texas, Austin)

The shear flow instabilities under the presence of magnetic fields in the protoplanetary disk can greatly facilitate the formation of density structures that serve as seeds prior to the onset of the gravitational Jeans instability. Such a seeding process may explain several outstanding puzzles in the planetary genesis that are further compounded by the new discoveries of extrasolar planets and a new insight into the equation of state of dense matter. This puzzle also includes the apparent narrow window of the age difference of the Sun and the Earth. We evaluate the effects of the Parker, magnetorotational(Balbus-Hawley), and kinematic dynamo instabilities by comparing the properties of these instabilities. We calculate the mass spectra of aggregated density structures by the above mechanism in the radial direction for an axisymmetric magnetohydrodynamic(MHD) torus equiblium and power-law density profile models. The mass spectrum of the magnetorotational instability may describe the origin of giant planets away from the central star such as Jupiter. Our local three-dimentional MHD simulation indicates that the coupling of the Parker and magnetorotational instabilities creates spiral arms and gas blobs in the accretion disk, reinforcing the theory and model.

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