Temperature Fluctuations driven by Magnetorotational Instability in Protoplanetary Disks

TL;DR

This study uses high-resolution simulations to reveal that magnetorotational instability causes significant local temperature fluctuations in protoplanetary disks, impacting mineral formation and disk conductivity.

Contribution

It demonstrates the importance of resolving current sheet structures to accurately model energy dissipation and thermal fluctuations in MRI-driven turbulence.

Findings

Order unity temperature variations driven by turbulent current sheets.

Higher resolution needed to accurately capture energy dissipation.

Temperature fluctuations influence mineral processing and disk conductivity.

Abstract

The magnetorotational instability (MRI) drives magnetized turbulence in sufficiently ionized regions of protoplanetary disks, leading to mass accretion. The dissipation of the potential energy associated with this accretion determines the thermal structure of accreting regions. Until recently, the heating from the turbulence has only been treated in an azimuthally averaged sense, neglecting local fluctuations. However, magnetized turbulence dissipates its energy intermittently in current sheet structures. We study this intermittent energy dissipation using high resolution numerical models including a treatment of radiative thermal diffusion in an optically thick regime. Our models predict that these turbulent current sheets drive order unity temperature variations even where the MRI is damped strongly by Ohmic resistivity. This implies that the current sheet structures where energy dissipation occurs must be well resolved to correctly capture the flow structure in numerical models. Higher resolutions are required to resolve energy dissipation than to resolve the magnetic field strength or accretion stresses. The temperature variations are large enough to have major consequences for mineral formation in disks, including melting chondrules, remelting calcium-aluminum rich inclusions, and annealing silicates; and may drive hysteresis: current sheets in MRI active regions could be significantly more conductive than the remainder of the disk.