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EVOLUTION DES DISQUES D'ACCRETION PROTOPLANETAIRES

Abstract : One of the most active fields of research in accretion disk theory is understanding the mechanisms that transport angular momentum outward. Two instabilities are thought to be responsible for it in massive, magnetized disks: the magnetorotational instability (MRI) caused by the presence of a weak magnetic field, and gravitational instabilities.

This PhD thesis is a study of the evolution of such disks. Global magnetohydrodynamical (MHD) simulations are performed, including a self-consistent calculation of the gravitational potential.

In the first section, we restrict the calculations to axisymmetry. By eliminating
from consideration the most unstable gravitational modes, these simulations
primarily highlight the behaviour of the MRI, with self--gravity serving to
modify the disk angular rotation profile.

The second section is fully three--dimensional. These simulations show that both
instabilities strongly interact with each other: MHD turbulence excites new modes
that interfere with the primary unstable gravitational mode already seen in
hydrodynamic simulations. As a result the accretion rate toward the central object
acquires a well--defined periodicity. In isothermal simulations, we find that
turbulence prevents the fragmentation of the disk and the formation of planets.

Finally, the last section describes 2D simulations studying the migration of an earth
type planet in a magnetized disk. The field is chosen to be toroidal, which in 2D is
MRI--stable. In agreement with recent analytical results, the presence of two magnetic resonances on either side of the planet orbit is demonstrated. These resonances modify the torque exerted on the planet by the disk. When the field strength decreases fast enough with radius, the results show that the planet migrates outward. This is a possible mechanism to halt type I migration in protoplanetary disks.
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Contributor : Sebastien Fromang <>
Submitted on : Wednesday, January 18, 2006 - 9:51:14 AM
Last modification on : Wednesday, December 9, 2020 - 3:11:28 PM
Long-term archiving on: : Saturday, April 3, 2010 - 9:30:25 PM

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  • HAL Id : tel-00011405, version 1

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Sebastien Fromang. EVOLUTION DES DISQUES D'ACCRETION PROTOPLANETAIRES. Astrophysique [astro-ph]. Université Paris-Diderot - Paris VII, 2004. Français. ⟨tel-00011405⟩

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