Vortex cycles at the inner edges of dead zones in protoplanetary disks

¹ Laboratoire AIM, CEA/DSM–CNRS–Université Paris 7, Irfu/Service d’Astrophysique, CEA-Saclay, 91191 Gif-sur-Yvette, France
e-mail: julien.faure@cea.fr
² Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Centre for Mathematical Sciences, Wilberforce Road, Cambridge, CB3 0WA, UK

Received: 8 May 2014
Accepted: 11 November 2014

Abstract

Context. In protoplanetary disks, the inner boundary between the turbulent and laminar regions is a promising site for planet formation because solids may become trapped at the interface itself or in vortices generated by the Rossby wave instability. The disk thermodynamics and the turbulent dynamics at that location are entwined because of the importance of turbulent dissipation to thermal ionization and, conversely, of thermal ionization to turbulence. However, most previous work has neglected this dynamical coupling and have thus missed a crucial element of the physics in this region.

Aims. In this paper, we aim to determine how the interplay between ionization and turbulence affects the formation and evolution of vortices at the interface between the active and the dead zones.

Methods. Using the Godunov code RAMSES, we performed a 3D magnetohydrodynamic global numerical simulation of a cylindrical model of an MRI-turbulent protoplanetary disk, including thermodynamical effects and a temperature-dependant resistivity. The comparison with an analogous 2D viscous simulation was extensively used to help identify the relevant physical processes and the disk’s long-term evolution.

Results. We find that a vortex forms at the interface as a result of Rossby wave instability, migrates inward, and penetrates the active zone where it is destroyed by turbulent motions. Subsequently, a new vortex emerges a few tens of orbits later at the interface, and the new vortex migrates inward too. The sequence repeats itself, resulting in cycles of vortex formation, migration, and disruption. This surprising behaviour is successfully reproduced using two different codes. We characterize this vortex life cycle and discuss its implications for planet formation at the dead-active interface. Our results also call for a better understanding of vortex migration in complex thermodynamical environments.

Conclusions. Our simulations highlight the importance of thermodynamical processes for the vortex evolution at the dead zone inner edge.