ASTR 170B2 Lecture Notes - Lecture 13: Low Mass, Jeans Instability, Minimum Mass
13 Oct 2017
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Document Summary
Star formation in the mw is - 3 msun per year. Only 2 % of a star forming region is converted to stars. Stars form in clouds of molecular hydrogen h2 located within the lower density atomic gas that makes up the interstellar medium. Giant molecular clouds are -30 --300 light years across, containing 10^4 to 10^7 solar masses of gas. Roughly 4000 of these in the milky way. Most of the matter in these star-forming clouds is in the form of molecules like h2and co. The amount of co is small compared to. The tipping point in mass is call the jean"s mass: For t ~ 30k and n = 300 molecules / cm3. Mjeans~ 18 msun sqrt (30^3 / 300) = A single cloud can potentially form many stars! A typical molecular cloud (t~ 30 k, n~ 300 particles/cm3) must contain. > ~ 170 solar masses for gravity to overcome pressure.
