Vortex migration in protoplanetary disks

TL;DR

This paper investigates how vortices in protoplanetary disks migrate due to asymmetries in their induced spiral waves, revealing rapid migration that could influence planet formation.

Contribution

It demonstrates that vortex-induced spiral wave asymmetries cause significant vortex migration, a process previously not well understood in protoplanetary disks.

Findings

Vortices induce density waves similar to planetary wakes.

Asymmetries lead to angular momentum exchange and migration.

Migration can occur on a timescale of a few thousand orbits.

Abstract

We consider the radial migration of vortices in two-dimensional isothermal gaseous disks. We find that a vortex core, orbiting at the local gas velocity, induces velocity perturbations that propagate away from the vortex as density waves. The resulting spiral wave pattern is reminiscent of an embedded planet. There are two main causes for asymmetries in these wakes: geometrical effects tend to favor the outer wave, while a radial vortensity gradient leads to an asymmetric vortex core, which favors the wave at the side that has the lowest density. In the case of asymmetric waves, which we always find except for a disk of constant pressure, there is a net exchange of angular momentum between the vortex and the surrounding disk, which leads to orbital migration of the vortex. Numerical hydrodynamical simulations show that this migration can be very rapid, on a time scale of a few thousand orbits, for vortices with a size comparable to the scale height of the disk. We discuss the possible effects of vortex migration on planet formation scenarios.