Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dda....38.0603h&link_type=abstract
American Astronomical Society, DDA meeting #38, #6.03
Astronomy and Astrophysics
Astronomy
Scientific paper
The gravitational instability model of the formation of planetesimals requires the density of solid particles in the central plane of the nebula to be enhanced and reach a critical value. As suggested by Youdin and Shu (2002), the gas-drag induced drift of small objects results in their pile up and provides the solid density enhancement necessary to trigger gravitational instability. However, as indicated by Weidenschilling (2003), the velocity difference between gas molecules and solid particles (due to the gas pressure gradients) affects the collective motion of solid objects and creates turbulence. The latter inhibits the accumulation of small bodies and prevents the disk to reach its critical density. During the evolution of a nebula, however, regions may appear where the velocity differences between gas and solids do not exist and turbulence will not occur. These regions are places where the density of the gas is locally enhanced. The combined effect of gas-drag and pressure gradient causes small objects, in the vicinity of such gas-density enhanced regions, to migrate towards and accumulate at the locations of the maximum gas pressure. However, since at these locations, the pressure gradient is non-existence, gas molecules and solid particles will have similar velocities, and small particles accumulated at these regions will not be subject to turbulence. As a result, the local density of the disk's solids at these regions will be enhanced and may reach the critical value necessary to trigger gravitational instability. I will present the results of the simulations of the formation of such solid-density enhanced regions and discuss the formation of planetesimals via gravitational instability in such environments.
This work is supported by the NASA Astrobiology Institute under the cooperative agreement NNA04CC08A at the Institute for Astronomy at the University of Hawaii.
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