Viscous Instability Triggered by Layered Accretion in Protoplanetary Disks

Abstract

Layered accretion is one of the inevitable ingredients in protoplanetary disks when disk turbulence is excited by magnetorotational instabilities (MRIs). In the accretion, disk surfaces where MRIs fully operate have a high value of disk accretion rate ($\dot{M}$), while the disk midplane where MRIs are generally quenched ends up with a low value of $\dot{M}$. Significant progress on understanding MRIs has recently been made by a number of dedicated MHD simulations, which requires improvement of the classical treatment of $\alpha$ in 1D disk models. To this end, we obtain a new expression of $\alpha$ by utilizing an empirical formula that is derived from recent MHD simulations of stratified disks with Ohmic diffusion. It is interesting that this new formulation can be regarded as a general extension of the classical $\alpha$. Armed with the new $\alpha$, we perform a linear stability analysis of protoplanetary disks that undergo layered accretion, and find that a viscous instability can occur around the outer edge of dead zones. Disks become stable in using the classical $\alpha$. We identify that the difference arises from $\Sigma -$dependence of $\dot{M}$; whereas $\Sigma$ is uniquely determined for a given value of $\dot{M}$ in the classical approach, the new approach leads to $\dot{M}$ that is a multi-valued function of $\Sigma$. We confirm our finding both by exploring a parameter space as well as by performing the 1D, viscous evolution of disks. We finally discuss other non-ideal MHD effects that are not included in our analysis, but may affect our results.

9 pages, 4 figures, accepted for publication in ApJ

References in corpus (9)

• Gaps, Rings, and Non-Axisymmetric Structures in Protoplanetary Disks - From Simulations to ALMA Observations
• Impact of dimensionless numbers on the efficiency of MRI-induced turbulent transport
• Grain Retention and Formation of Planetesimals near the Snow Line in MRI-driven Turbulent Protoplanetary Disks
• MHD simulations of the magnetorotational instability in a shearing box with zero net flux. I. The issue of convergence
• Hall-effect Controlled Gas Dynamics in Protoplanetary Disks: II. Full 3D Simulations toward the Outer Disk
• Magnetically driven accretion in protoplanetary discs
• Magnetic Flux Concentration and Zonal Flows in Magnetorotational Instability Turbulence
• Simulations of Magnetorotational Turbulence with a Higher-Order Godunov Scheme
• Global evolution of the magnetic field in a thin disc and its consequences for protoplanetary systems

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• Self-Sustaining Vortices in Protoplanetary Disks: Setting the Stage for Planetary System Formation
• The role of density perturbation on planet formation by pebble accretion