Astronomy
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Item Planetesimal clusters in a Keplerian disk I. gravitational evolution(EDP Sciences, 2002-08-30) Tanga, P.; Michel, P.; Richardson, D. C.It was recently demonstrated by numerical simulations that a turbulent flow in a rotating system is capable of efficiently concentrating passively advected particles having a density larger than the fluid – inside anti-cyclonic vortices. This process has important consequences on the distribution of solid particles in protoplanetary disks, since dust surface densities 1–2 orders of magnitude higher than the background are rapidly reached in vortex cores. However, until now, the role of self-gravitation of captured solids has been neglected. In this work we study the action of mutual gravitational interactions - after the gas has dissipated - over the dynamics of planetesimals inside clusters similar to those created in vortex cores. A comparison is made between the behavior of idealized clusters of planetesimals characterized by ad-hoc velocity profiles, and more complex initial conditions such as those obtained in previous hydrodynamical simulations. We show here that, within the explored interval of parameters, mutual scattering of particles can quickly disperse the cluster. Our results are demonstrated to be not dependent on the resolution employed. It can be concluded that if large planetesimals were formed inside vortex cores, they would be ejected by mutual perturbations.Item Gravitational instability and clustering in a disk of planetesimals(EDP Sciences, 2004-08-05) Tanga, P.; Weidenschilling, S. J.; Michel, P.; Richardson, D. C.For a long time, gravitational instability in the disk of planetesimals has been suspected to be the main engine responsible for the beginning of dust growth, its advantage being that it provides for rapid growth. Its real importance in planetary formation is still debated, mainly because the potential presence of turbulence can prevent the settling of particles into a gravitationally unstable layer. However, several mechanisms could yield strongly inhomogeneous distributions of solids in the disk: radial drift, trapping in vortices, perturbations by other massive bodies, etc. In this paper we present a numerical study of a gravitationally unstable layer. This allows us to go beyond the classical analytical study of linear perturbations, exploring a highly non-linear regime. A hierarchical growth of structure in the presence of dissipation (gas drag) can yield large, virialized clusters of planetesimals, the first time such clusters have been observed in the context of planetesimal disks.