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

Several protoplanetary discs observed by ALMA show dust concentrations consistent with particle trapping in giant vortices. The formation and survival of vortices are 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 discs 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 disc is often neglected as the discs azimuth is limited to Δϕ ≤ π/2.We aim to investigate the influence of the azimuthal extent of the disc on the long-term evolution of a protoplanetary disc and the possibility of large vortices forming. To this end, we perform 3D simulations for up to 1000 local orbits using different values of Δϕ = π/2 to 2p for VSI in discs with a prescribed radial density and temperature gradient cooling on short time-scales. We find the VSI capable of forming large vortices that can exist at least several hundred orbits in simulations covering a disc with Δϕ ≥ π. 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. © 2018 The Author(s).