Transport in Gravitationally Unstable Protoplanetary Disks: Slings, Swings, and Rings

During early phases of a protoplanetary disk’s life, gravitational instabilities (GIs) can produce significant mass and angular momentum transport, dramatically alter disk structure, mix and shock-process gas and solids, and may be instrumental in planet formation. We present a grid-based 3D hydrodynamics convergence study of a protoplanetary disk orbiting a 0.5 solar-mass star as it settles into a quasi-steady asymptotic state where approximate balance exists between heating produced by GIs and cooling governed by realistic dust opacities. We assess disk stability criteria, thermodynamic properties, strengths of GIs, characteristics of density waves and torques produced by GIs, the radial mass transport arising from these torques, and the level to which transport can be represented as a local or global process. Convergence characteristics for most physical and thermal processes display distinct differences between inner optically thick and outer optically thin regions of the disk. Torques in the inner region are dominated by low-order Fourier components of the azimuthal mass distribution. These torques are strongly variable on the local dynamical times and driven by recurrent swing amplification. In the outer region, sling amplified m =1 torques dominate. Ring-like structures exhibiting strong noncircular motions and vortices develop between 8 and 14 au. If real, these may play a role in giant planet formation. We find that GIs are global structures and edges (optically thick/thin, cooling time gradients, real physical edges, radial Q variations, rings, ...) are important. Edges affect many physical processes that vary in time and space and illustrate the global nature of GIs.