Grain size control in dense interstellar clouds

Details Grain size control in dense interstellar clouds Grain size control in dense interstellar clouds

Mar 1977

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977a%26a....55..253s&link_type=abstract

Astronomy and Astrophysics, vol. 55, no. 2, Mar. 1977, p. 253-260.

Astronomy and Astrophysics

Astrophysics

40

Interstellar Matter, Particle Size Distribution, Protostars, Stellar Mass Accretion, Astrophysics, Collision Parameters, Grains, Gravitational Collapse, Radiation Pressure

Scientific paper

The efficiencies of various processes which may affect the grain-size distribution in dense interstellar clouds are investigated, concentrating on grain-grain collisions. Collision time scales are evaluated for the following processes that can lead to grain-grain collisions and coagulation: Brownian motion, inertial effects during gravitational collapse, radiation pressure from an embedded protostar, turbulence, and grain drift in a magnetic field. The results indicate that coagulation induced by the flow of gravitationally collapsing gas past the grains is negligible since the grains and gas become position-coupled long before coagulation can occur and that Brownian coagulation is only effective for the smallest grains present. It is suggested that the Brownian process is responsible for the anomalously low far-UV extinction observed in four objects. It is also found that radiation pressure appears to be effective only in the inner part of a dense molecular cloud containing an embedded protostar, that turbulence is an efficient grain-collision mechanism in interstellar clouds, and that electromagnetic grain drift may also be effective. Effects of grain shattering and vaporization are briefly discussed.

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