Vortex survival in 3D self-gravitating accretion discs

TL;DR

This study demonstrates that self-gravity in 3D accretion discs enhances vortex survival despite elliptic instabilities, with implications for dust trapping and planet formation in protoplanetary discs.

Contribution

It shows that even weak self-gravity can sustain 3D vortices over long timescales, revealing a new mechanism for vortex longevity in protoplanetary discs.

Findings

Self-gravity promotes vortex survival in 3D discs.

Vortices can grow secularly despite elliptic instability.

Vortices exhibit episodic bursts due to instability interactions.

Abstract

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.