Planetesimal formation in self-gravitating discs -- dust trapping by vortices

TL;DR

This study uses simulations to show that transient vortices in self-gravitating protoplanetary discs can effectively concentrate dust particles, promoting the formation of planetesimals by gravitational collapse.

Contribution

It demonstrates that anticyclonic vortices are highly efficient at trapping dust, significantly enhancing planetesimal formation in massive self-gravitating discs.

Findings

Vortices concentrate small and intermediate dust particles effectively.

Density enhancements can surpass those in spiral density waves.

Enhanced dust concentration accelerates gravitational collapse into planetesimals.

Abstract

The mechanism through which meter-sized boulders grow to km-sized planetesimals in protoplanetary discs is a subject of active research, since it is critical for planet formation. To avoid spiralling into the protostar due to aerodynamic drag, objects must rapidly grow from cm-sized pebbles, which are tightly coupled to the gas, to large boulders of 1-100m in diameter. It is already well known that over-densities in the gaseous component of the disc provide potential sites for the collection of solids, and that significant density structures in the gaseous component of the disc (e.g., spiral density waves) can trap solids efficiently enough for the solid component of the disc to undergo further gravitational collapse due to their own self-gravity. In this work, we employ the PENCIL CODE to conduct local shearing sheet simulations of massive self-gravitating protoplanetary discs, to study the effect of anticyclonic transient vortices, or eddies, on the evolution of solids in these discs. We find that these types of structures are extremely efficient at concentrating small and intermediate-sized dust particles with friction times comparable to, or less than, the local orbital period of the disc. This can lead to significant over-densities in the solid component of the disc, with density enhancements comparable to, and even higher, than those within spiral density waves; increasing the rate of gravitational collapse of solids into bound structures.