Vortices in stratified protoplanetary disks

Abstract

Context. Large-scale vortices could play a key role in the evolution of protoplanetary disks, particularly in the dead-zone where no turbulence associated with magnetic field is expected. Their possible formation by the subcritical baroclinic instability is a complex issue because of the vertical structure of the disk and the elliptical instability. Aims. In 2D disks the baroclinic instability is studied as a function of the thermal transfer efficiency. In three-dimensional disks we explore the importance of radial and vertical stratification on the processes of vortex formation and amplification. Methods. Numerical simulations are performed using a fully compressible hydrodynamical code based on a second-order finite volume method. We assume a perfect gas law in inviscid disk models in which heat transfer is due to either relaxation or diffusion. Results. In 2D, the baroclinic instability with thermal relaxation leads to the formation of large-scale vortices, which are unstable with respect to the elliptic instability. In the presence of heat diffusion, hollow vortices are formed which evolve into vortical structures with a turbulent core. In 3D, the disk stratification is found to be unstable in a finite layer which can include the mid-plane or not. When the unstable layer contains the mid-plane, the 3D baroclinic instability with thermal relaxation is found to develop first in the unstable layer as in 2D, producing large-scale vortices. These vortices are then stretched out in the stable layer, creating long-lived columnar vortical structures extending through the width of the disk. They are also found to be the source of internal vortex layers that develop across the whole disk along baroclinic critical layer surfaces, and form new vortices in the upper region of the disk. Conclusions. In 3D disks, vortices can survive for a very long time if the production of vorticity by the baroclinic amplification balances the destruction of vorticity by the elliptical instability. However, this possibility is strongly dependent on the disk properties. Such baroclinic vortices could play a significant role in the global disk evolution and in participating to the decoupling of solids from the gas component. They could also contribute to the formation of new out-of-plane vortices by a critical layer excitation mechanism.

Gravitational slopes, geomorphology, and material strengths of the nucleus of comet 67P/Churyumov-Gerasimenko from OSIRIS observations

“…This value is remarkably consistent with our results (Table 1), particularly if we take into account a compaction scenario where the primordial material was even weaker. Our results therefore tend to favor a formation of comets by pebble accretion in a region of higher concentration of particles such as vortices (Johansen et al 2014;Barge & Sommeria 1995;Blum et al 2014), which implies a gentle formation process by accretion at low velocity, on the order of 1 m s −1 or lower. In contrast, the hierarchical accretion model (Weidenschilling 2004) with velocities up to 50 m s −1 for particles larger than 1 m, and the collisional scenario between two large bodies of tens of km or more (Davis & Farinella 1997) with an internal compression by gravity larger than 10 kPa, although not excluded, are less favored.…”

Oscillatory migration of accreting protoplanets driven by a 3D distortion of the gas flow

“…Regarding the baroclinic perturbations, although they are known to produce vortical instabilities in protoplanetary disks (Klahr & Bodenheimer 2003;Petersen et al 2007a,b;Lesur & Papaloizou 2010;Raettig et al 2013;Barge et al 2016), they have been rarely considered in relation to hot protoplanets. For example, Owen & Kollmeier (2017) claim that that hot protoplanets can excite large-scale baroclinic vortices but we do not identify any of those in our simulations.…”

Gaps and rings carved by vortices in protoplanetary dust

“…The code was previously used to study the formation of vortices by the Rossby-Wave or the baroclinic instability (Richard et al 2013;Barge et al 2016), and also to study the coupled evolution of gas and dust (Inaba & Barge 2006). This code, which uses the finite volume method and was first presented in Inaba et al (2005) can maintain high accuracy over large integration periods (Surville & Barge 2015;Surville et al 2016).…”