A method for coupling dynamical and collisional evolution of dust in circumstellar disks: the effect of a dead zone

TL;DR

This paper introduces a hybrid simulation method coupling dynamical and collisional evolution of dust in circumstellar disks, revealing how dead zones influence dust growth and pebble formation in protoplanetary disks.

Contribution

A new hybrid lagrangian/eulerian code is developed to simulate dust evolution, explicitly coupling collisional and dynamical processes in circumstellar disks.

Findings

Dust growth is rapid, with particles reaching millimeter sizes without dead zones.

Dead zones significantly enhance coagulation, forming 1cm-10cm pebbles.

Pebbles can accumulate into larger bodies within turbulent structures.

Abstract

Dust is a major component of protoplanetary and debris disks as it is the main observable signature of planetary formation. However, since dust dynamics is size-dependent (because of gas-drag or radiation pressure) any attempt to understand the full dynamical evolution of circumstellar dusty-disks that neglect the coupling of collisional evolution with dynamical evolution is thwarted because of the feedback between these two processes. Here, a new hybrid lagrangian/eulerian code is presented that overcomes some of these difficulties. The particles representing "dust-clouds" are tracked individually in a lagrangian way. This system is then mapped on an eulerian spatial grid, inside the cells of which the local collisional evolutions are computed. Finally, the system is remapped back in a collection of discrete lagrangian particles keeping constant their number. An application example on dust growth in a turbulent protoplanetary disk at 1 AU is presented. First the growth of dust is considered in the absence of a dead-zone and the vertical distribution of dust is self-consistently computed. It is found that the mass is rapidly dominated by particles about a fraction of millimeter in size. Then the same case with an embedded dead-zone is investigated and It is found that coagulation is much more efficient and produces, in a short time scale, 1cm-10cm dust pebbles that dominate the mass. These pebbles may then be accumulated into embryos sized objects inside large-scale turbulent structures as shown recently (see e.g. Johansen et al., 2007).