Radial and vertical angular momentum transport in protostellar discs

Abstract

Angular momentum in protostellar discs can be transported either radially, through turbulence induced by the magnetorotational instability (MRI), or vertically, through the torque exerted by a large-scale magnetic field. We present a model of steady-state discs where these two mechanisms operate at the same radius and derive approximate criteria for their occurrence in an ambipolar diffusion dominated disc. We obtain "weak field'' solutions - which we associate with the MRI channel modes in a stratified disc - and transform them into accretion solutions with predominantly radial angular-momentum transport by implementing a turbulent-stress prescription based on published results of numerical simulations. We also analyze "intermediate field strength'' solutions in which both radial and vertical transport operate at the same radial location. Our results suggest, however, that this overlap is unlikely to occur in real discs.

5 pages, 2 figures, 1 table, aastex.cls. Accepted for publication in Astrophysics & Space Science

References in corpus (12)

• Angular Momentum Transport by MHD Turbulence in Accretion Disks: Gas Pressure Dependence of the Saturation Level of the Magnetorotational Instability
• The Balbus-Hawley instability in weakly ionised discs
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• The Effect of the Hall Term on the Nonlinear Evolution of the Magnetorotational Instability: I. Local Axisymmetric Simulations
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• Launching of jets and the vertical structure of accretion disks
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• Self-similar Collapse of Rotating Magnetic Molecular Cloud Cores
• Magnetorotational instability in protoplanetary discs
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• Are Magnetic Wind-Driving Disks Inherently Unstable?

Cited by in corpus (2)

• Numerical simulations of the Princeton magneto-rotational instability experiment with conducting axial boundaries
• Structure of Protoplanetary Discs with Magnetically-driven Winds