Gravito-turbulence and dynamo in poorly ionized protostellar discs – I. Zero-net-flux case

ABSTRACT In their early stages, protoplanetary discs are sufficiently massive to undergo gravitational instability (GI). This instability is thought to be involved in mass accretion, planet formation via gas fragmentation, the generation of spiral density waves, and outbursts. A key and very recent...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2021-09, Vol.506 (1), p.1407-1426
Main Authors: Riols, A, Xu, W, Lesur, G, Kunz, M W, Latter, H
Format: Article
Language:English
Subjects:
ASTRONOMY AND ASTROPHYSICS
Astrophysics
dynamo
instabilities
Physics
protoplanetary discs
turbulence
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Summary:ABSTRACT In their early stages, protoplanetary discs are sufficiently massive to undergo gravitational instability (GI). This instability is thought to be involved in mass accretion, planet formation via gas fragmentation, the generation of spiral density waves, and outbursts. A key and very recent area of research is the interaction between the GI and magnetic fields in young protoplanetary discs, in particular whether this instability is able to sustain a magnetic field via a dynamo. We conduct 3D, stratified shearing-box simulations using two independent codes, PLUTO and Athena++, to characterize the GI dynamo in poorly ionized protostellar discs subject to ambipolar diffusion. We find that the dynamo operates across a large range of ambipolar Elssaser number Am (which characterizes the strength of ambipolar diffusion) and is particularly strong in the regime Am = 10–100, with typical magnetic to thermal energy ratios of order unity. The dynamo is only weakly dependent on resolution (at least for Am ≲ 100), box size, and cooling law. The magnetic field is produced by the combination of differential rotation and large-scale vertical roll motions associated with spiral density waves. Our results have direct implications for the dynamo process in young protoplanetary discs and possibly some regions of active galactic nucleus discs.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stab1637