Transition region from turbulent to dead zone in protoplanetary disks: local shearing box simulations

TL;DR

This study uses local shearing box simulations to analyze the transition from turbulent to dead zones in protoplanetary disks, revealing how resistivity influences turbulence and magnetic activity at the boundary.

Contribution

It provides a detailed numerical investigation of the boundary between active and dead zones, highlighting the role of resistivity and turbulence penetration in protoplanetary disks.

Findings

Turbulence is inhibited in regions with high resistivity.

Magnetic activity and density fluctuations occur at the dead zone boundaries.

Turbulent cascade follows Kolmogorov scaling in the dead zone.

Abstract

The dynamical evolution of protoplanetary disks is of key interest for building a comprehensive theory of planet formation and to explain the observational properties of these objects. Using the magnetohydrodynamics code Athena++, with an isothermal shearing box setup, we study the boundary between the active and dead zone, where the accretion rate changes and mass can accumulate. We quantify how the turbulence level is affected by the presence of a non uniform ohmic resistivity in the radial-x direction that leads to a region of inhibited turbulence (or dead zone). Comparing the turbulent activity to that of ideal simulations, the turbulence inhibited area shows density fluctuations and magnetic activity at its boundaries, driven by energy injection from the active (ideal) zone boundaries. We find magnetic dissipation to be significantly stronger in the ideal regions, and the turbulence penetration through the boundary of the dead zone is determined by the value of the resistivity itself, through the ohmic dissipation process, though the thickness of the transition does not play a significant role in changing the dissipation. We investigate the 1D spectra along the shearing direction: magnetic spectra appear flat at large scales both in ideal as well as resistive simulations, though a Kolmogorov scaling over more than one decade persists in the dead zone, suggesting the turbulent cascade is determined by the hydrodynamics of the system: MRI dynamo action is inhibited where sufficiently high resistivity is present.