Vortex Survival Research Articles

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

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.

Vortex survival in 3D self-gravitating accretion discs

Large-scale, dust-trapping vortices may account for observations of asymmetric protoplanetary discs. Disc vortices are also potential sites for accelerated planetesimal formation by concentrating dust grains. However, in 3D discs vortices are subject to destructive `elliptic instabilities', which reduces their viability as dust traps. The survival of vortices in 3D accretion discs is thus an important issue to address. In this work, we perform shearing box simulations to show that disc self-gravity enhances the survival of 3D vortices, even when self-gravity is weak in the classic sense (e.g. with a Toomre $Q\simeq5$). We find a 3D, self-gravitating vortex can grow on secular timescales in spite of the elliptic instability. The vortex aspect-ratio decreases as it strengthens, which feeds the elliptic instability. The result is a 3D vortex with a turbulent core that persists for $\sim 10^{3}$ orbits. We find when gravitational and hydrodynamic stresses become comparable, the vortex may undergo episodic bursts, which we interpret as interaction between elliptic and gravitational instabilities. We estimate the distribution of dust particles in self-gravitating, turbulent vortices. Our results suggest large-scale vortices in protoplanetary discs are more easily observed at large radii.

Elliptic and magneto-elliptic instabilities

Vortices are the fundamental units of turbulent flow. Understanding their stability properties therefore provides fundamental insights on the nature of turbulence itself. In this contribution I briely review the phenomenological aspects of the instability of elliptic streamlines, in the hydro (elliptic instability) and hydromagnetic (magneto-elliptic instability) regimes. Vortex survival in disks is a balance between vortex destruction by these mechanisms, and vortex production by others, namely, the Rossby wave instability and the baroclinic instability.