Grain evolution in dark clouds
B. T. Draine;
In Protostars and planets II, 1985, Tucson, AZ, University of Arizona Press, p. 621
ABSTRACT:Observations pertaining to the sizes and composition of grains in diffuse clouds and dark clouds are briefly reviewed.
The
physical processes acting to change the composition and size distribution of
grains in dark clouds are examined.
Accretion of ice mantles on grains can
deplete molecules from the gas phase on time scales short compared to cloud
lifetimes.
Temperature fluctuations can prevent mantle formation only on very small (radii of
about 10 A or less) grains.
Turbulence-driven coagulation may act to remove
the smaller grains from the grain size distribution, resulting in grains
of a conglomerate character; however, whether or not grains colliding at
0.01-0.1 km/s will actually stick together is uncertain.
Fragmentation
following high-velocity grain-grain collisions (e.g., induced in shock waves)
may replenish the small particles, and sputtering of grains in shock waves
can erode ice mantles.
The FU Orionis phenomenon in active star-forming
clouds may act to sublime ice mantles and return molecules to the gas phase, but
is probably of secondary importance.
KEYWORDS: cosmic dust, interstellar matter, molecular clouds, molecular spectra, particle size distribution, protostars, shock waves, supernovae
PERSOKEY:dust, ,
CODE: draine85a