AST 341 Lecture Notes - Lecture 24: Main Sequence, Molecular Cloud, Metallicity
25 Dec 2016
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Document Summary
To summarize what we have learned so far: the jeans mass yields the condition for which gravitational collapse can start. What we need to discuss next is what happens during the collapse itself. During the early stages, the collapse is isothermal (i. e. t =constant), the gas is optically thin and it cools e ciently due to radiation from molecules such as carbon monoxide. If t stays constant while increases, then gravity becomes even more dominant over pressure and the characteristic jeans mass for the cloud hence drops (mj t 3/2 1/2). This allows for the possibility that the cloud might break up into smaller fragments during the collapse itself. If this happens, then each fragment will start collapsing on its own. The collapse of the cloud (or each of its fragments) slows or halts once the gas becomes optically thick and cooling becomes ine cient due to the fact that radiation is unable to freely escape.
