Dust-trapping Rossby vortices in protoplanetary disks

Abstract

Context. One of the most challenging steps in planet formation theory is the one leading to the formation of planetesimals of kilometre size. A promising scenario involves the existence of vortices able to concentrate a large amount of dust and grains in their centres. Up to now this scenario has mostly been studied in 2D razor thin disks. A 3D study including, simultaneously, the formation and resulting dust concentration of the vortices with vertical settling, is still missing. Aims. The Rossby wave instability self-consistently forms 3D vortices, which have the unique quality of presenting a large-scale vertical velocity in their centre. Here we aim to study how this newly discovered effect can alter the dynamic evolution of the dust. Methods. We performed global 3D simulations of the RWI in a radially and vertically stratified disk using the code MPI-AMRVAC. After the growth phase of the instability, the gas and solid phases are modelled by a bi-fluid approach, where the dust is considered as a fluid without pressure. Both the drag force of the gas on the dust and the back reaction of the dust on the gas are included. Multiple grain sizes from 1 mm to 5 cm are used with a constant density distribution. Results. We obtain in a short timescale a high concentration of the largest grains in the vortices. Indeed, in 3 rotations the dust-to-gas density ratio grows from 10 −2 to unity leading to a concentration of mass up to that of Mars in one vortex. The presence of the radial drift is also at the origin of a dust pile-up at the radius of the vortices. Lastly, the vertical velocity of the gas in the vortex causes the sedimentation process to be reversed, the mm size dust is lifted and higher concentrations are obtained in the upper layer than in the midplane. Conclusions. The Rossby wave instability is a promising mechanism for planetesimal formation, and the results presented here can be of particular interest in the context of future observations of protoplanetary disks.

Planet-vortex interaction: How a vortex can shepherd a planetary embryo

“…Meheut et al (2012b) show that large dust particles can greatly affect their parent vortices. Thus, a more complete work is needed to answer the question of whether a vortex can maintain its shape while growing a planet.…”

Interpreting Brightness Asymmetries in Transition Disks: Vortex at Dead Zone or Planet-carved Gap Edges?

“…Formation of a large-scale vortex can be triggered in protoplanetary disks due to baroclinic instability (Klahr & Bodenheimer 2003;Lyra & Klahr 2011;Raettig et al 2013;Lyra 2014) or the Rossby wave instability (RWI) via the coagulation of smaller-scale vortices (Lovelace et al 1999;Li et al 2000Li et al , 2001Lyra et al 2009b;Meheut et al 2010Meheut et al , 2012aMeheut et al , 2012bMeheut et al , 2012cMeheut et al , 2013Richard et al 2013;Flock et al 2015). Barge & Sommeria (1995) and Klahr & Henning (1997) have already shown that particles tend to get trapped in anticyclonic vortices.…”

Efficiency of coherent vortices to trap dust particles in the solar nebula

“…These papers have addressed the formation of the vortices, their stability and their interaction with dust particles. We refer for example to Meheut et al [5] for a recent study and for up-to-date references.…”