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A.N. Youdin (Princeton University)
The formation of planetesimals by gravitational instabilities (GI) of small solids is opposed by turbulent stirring. While traditional GI criteria such as the Roche density are difficult to satisfy, dissipation by gas drag modifies stability properties. The transfer of angular momentum from solids to gas allows dissipative GI at lower densities, higher velocity dispersions, and longer wavelengths. Collapse is slow compared to orbital times, and initially occurs in rings whose non-linear fragmentation determine planetesimal size. Turbulent stirring must still be weak enough that growth is faster than disk lifetimes or particle drift rates. This requires turbulent diffusivities, "alpha" < 10-6-10-3, depending on the disk model. Growth depends on the the strength of turbulence, the surface density of self-gravitating solids, and the strength of drag coupling (itself a function of gas density and particle size). Radial variations of the growth rate has implications for the formation of short period extrasolar planets and the outer edge of the primordial Kuiper Belt.
This material is based on work supported by NASA under grant NAG5-11664.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.