The dust to gas ratio in a nebula is unstable in the presence of a radiation field. A radiative analogue of the Jeans’ critical mass for gas exists, from which it appears that in a molecular cloud environment the dust tends to accumulate into discrete concentrations of mass ~ 1015 – 1023 g. Solid bodies of cometary or asteroidal dimensions may therefore comprise a significant component of the interstellar medium. The implications of this interstellar population for theories of star formation are briefly discussed. Evidence is presented that some proportion of the comet population, including Halley’s Comet, may have been recently captured during passage of the Solar System through the Scorpio-Centaurus association.
KeywordsSolar System Radiation Pressure Interstellar Medium Molecular Cloud Oort Cloud
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