Vortex formation and survival in protoplanetary discs subject to vertical shear instability

Abstract

Several protoplanetary disks observed by ALMA show dust concentrations consistent with particle trapping in giant vortices. The formation and survival of vortices is of major importance for planet formation, because vortices act as particle traps and are therefore preferred locations of planetesimal formation. Recent studies showed that the vertical shear instability (VSI) is capable of generating turbulence and small vortices in protoplanetary disks that have the proper radial and vertical stratification and thermally relax on sufficiently short time scales. But the effect of the azimuthal extend of the disk is often neglected as the disks azimuth is limited to $\Delta \phi \leq \pi/2$. We aim to investigate the influence of the azimuthal extent of the disk on the long-term evolution of a protoplanetary disk and the possibility of large vortices forming. To this end, we perform 3-dimensional simulations for up to 1000 local orbits using different values of $\Delta \phi = \pi/2 $ to $2\pi$ for VSI in disks with a prescribed radial density and temperature gradient cooling on short timescales. We find the VSI capable of forming large vortices which can exist at least several hundred orbits in simulations covering a disk with $\Delta \phi \geq \pi$. This suggests the VSI to be capable to form vortices or at least to trigger vortex formation via a secondary instability, e.g. Rossby Wave Instability or Kelvin Helmholtz Instability.