Year: 2018
Type: article
Abstract: Via the process of accretion, magnetorotational turbulence removes energy from a disc's orbital motion and transforms it into heat. Turbulent heating is far from uniform and is usually concentrated in small regions of intense dissipation, characterized by abrupt magnetic reconnection and higher temperatures. These regions are of interest because they might generate non-thermal emission, in the form of flares and energetic particles, or thermally process solids in protoplanetary discs. Moreover, the nature of the dissipation bears on the fundamental dynamics of the magnetorotational instability (MRI) itself: local simulations indicate that the large-scale properties of the turbulence (e.g. saturation levels and the stress–pressure relationship) depend on the short dissipative scales. In this paper we undertake a numerical study of how the MRI dissipates and the small-scale dissipative structures it employs to do so. We use the Godunov code ramses and unstratified compressible shearing boxes. Our simulations reveal that dissipation is concentrated in ribbons of strong magnetic reconnection that are significantly elongated in azimuth, up to a scale height. Dissipative structures are hence meso-scale objects, and potentially provide a route by which large scales and small scales interact. We go on to show how these ribbons evolve over time – forming, merging, breaking apart, and disappearing. Finally, we reveal important couplings between the large-scale density waves generated by the MRI and the small-scale structures, which may illuminate the stress–pressure relationship in MRI turbulence.
DOI: 10.1093/mnras/sty791
Authors: Johnathan Ross, Henrik N Latter
Institution: University of Cambridge
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2790334336