Astronomy
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Item The pursuit of the whole NChilada: Virtual petaflops using multi-adaptive algorithms for gravitational systems(IBM, 2004) Lake, G.; Quinn, T.; Richardson, D. C.; Stadel, J.We describe the keys to meeting the challenges of N-body simulation: adaptive potential solvers, adaptive integration, and volume renormalization. With these techniques and a dedicated teraflop facility, simulation can keep pace with observations of the universe. We also describe some problems in simulating the formation and stability of planetary systems.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.