Forming stars from molecular Hydrogen clouds

Forming stars from molecular Hydrogen clouds - Forming...

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Unformatted text preview: Forming stars from molecular Hydrogen clouds Because of its size, the collapsing molecular cloud must fragment, or there would be one immense, very short-lived sun. (Sometimes this happens - large fragments of so-called "prestellar nebulae" with masses around 20M S , collapse to a star, which lasts about 1Ma and then goes nova. In comparison, note that a sol-type sun lasts 10 10 years.) What causes the fragmentation? It could be turbulence, pressure waves or differential cooling. One can calculate that there is a minimum mass (at a given temperature and density) called the Jean's Mass, needed for an individual star to collapse. For a given medium, the larger the mass the more likely the collapse. Hence stars form in preference to planets, and we assume planetary formation follows formation of the sun. The fact that there is a tendency for fragmentation then stellar formation means that stars often form in "star clusters". There must be a dispersal mechanism though, at least in some cases, as 5-form in "star clusters"....
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