The formation of comets in wind-driven shells around protostars |
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| Institution: | 1. Laboratoire Lagrange, Université Cote d''Azur, CNRS, Observatoire de la Côte d''Azur, Boulevard de l''Observatoire, 06304 Nice Cedex 4, France;2. Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, 48149, Germany;3. Department of Space Studies, Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, USA;4. David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto, 50 St George St, Toronto, ON M5S 3H4, Canada;5. Sidrat Research, 124 Merton St #507, Toronto, ON M4S 2Z2, Canada;6. Collège de France, CNRS, PSL Univ., Sorbonne Univ., 11 Pl. Berthelot, 75231 Paris, France |
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| Abstract: | It is shown that the dense, turbulent, decelerating shells produced by protostellar flows around young stars are a probable site for rapid grain growth by coalescing collisions. The growth of grains occurs in a thin dust layer at the leading edge of the gas shell until a critical grain size on the order of 1?10 μm is reached. Grains larger than this decouple from the turbulence and eventually reach sizes of ≈100 μm. These large grains form a thin dust shell with low-velocity dispersion, in which ultimately local gravitational instability takes place. This causes the accumulation of comet-sized aggregations of dust, assuming that the dust velocity dispersion is on the order of 10?2 m sec?1. It is proposed that the mechanism could lead to a high space density of comets in molecular clouds. The efficient formation of “giant” grains, and even comet nuclei, in the regions around young stars has important implications both for cometary astronomy and for understanding the dynamical and chemical evolution of molecular clouds and the interstellar medium. |
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