The Formation of Fragments at Corotation in Isothermal Protoplanetary Disks

TL;DR

This paper combines analytic reasoning and 3D simulations to show that in isothermal protoplanetary disks, gravitational fragmentation tends to initiate at corotation radii of spiral modes when the Toomre parameter is low.

Contribution

It provides a novel analytic explanation for the preferred formation sites of fragments at corotation radii, supported by hydrodynamics simulations.

Findings

Fragments form first at corotation radii of spiral modes

Low Toomre Q promotes gravitational instability

Simulation results support analytic predictions

Abstract

Numerical hydrodynamics simulations have established that disks which are evolved under the condition of local isothermality will fragment into small dense clumps due to gravitational instabilities when the Toomre stability parameter $Q$ is sufficiently low. Because fragmentation through disk instability has been suggested as a gas giant planet formation mechanism, it is important to understand the physics underlying this process as thoroughly as possible. In this paper, we offer analytic arguments for why, at low $Q$, fragments are most likely to form first at the corotation radii of growing spiral modes, and we support these arguments with results from 3D hydrodynamics simulations.