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

• Published in: arXiv.org
• Main Authors: Riols, A, W Xu, Lesur, G, Kunz, M W, Latter, H
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 07.06.2021
• Subjects: Accretion disks; Ambipolar diffusion; Density; Deposition; Differential rotation; Gravitational instability; Magnetic fields; Outbursts; Physics - Earth and Planetary Astrophysics; Physics - High Energy Astrophysical Phenomena; Planet formation; Protoplanetary disks; Protostars; Shearing; Star formation; Thermal energy
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2106.03607

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 three-dimensional, stratified shearing-box simulations using two independent codes, PLUTO and Athena++, to characterise the GI dynamo in poorly ionised protostellar discs subject to ambipolar diffusion. We find that the dynamo operates across a large range of ambipolar Elssaser number Am (which characterises 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 AGN discs.