Magnetorotational instability and dynamo action in gravitoturbulent astrophysical discs

Abstract

Though usually treated in isolation, the magnetorotational and gravitational instabilities (MRI and GI) may coincide at certain radii and evolutionary stages of protoplanetary discs and active galactic nuclei. Their mutual interactions could profoundly influence several important processes, such as accretion variability and outbursts, fragmentation and disc truncation, or large-scale magnetic field production. Direct numerical simulations of both instabilities are computationally challenging and remain relatively unexplored. In this paper, we aim to redress this neglect via a set of 3D vertically stratified shearing-box simulations, combining self-gravity and magnetic fields. We show that gravito-turbulence greatly weakens the zero-net-flux MRI. In the limit of efficient cooling (and thus enhanced GI), the MRI is completely suppressed, and yet strong magnetic fields are sustained by the gravitoturbulence. This turbulent `spiral wave' dynamo may have widespread application, especially in galactic discs. Finally, we present preliminary work showing that a strong net-vertical-flux revives the MRI and supports a magnetically dominated state, in which the GI is secondary.

23 pages, 16 figures, accepted in MNRAS

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• MHD accretion-ejection: jets launched by a non-isotropic accretion disk dynamo. I. Validation and application of selected dynamo tensorial components
• Eruptive Behavior of Magnetically Layered Protoplanetary Disks in Low Metallicity Environments
• Gravito-turbulence and dynamo in poorly ionised protostellar discs. I. Zero-net-flux case
• Magnetohydrodynamic convection in accretion discs
• Gravitoturbulent dynamo in global simulations of gaseous disks