GE CLST 70A Lecture Notes - Lecture 12: Spiral Galaxy, Large Magellanic Cloud, Nice Model
23 Jan 2017
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Document Summary
Friction in a rich disk causes material to spiral inwards. Friction decreases at the end, since only small amounts of material remain outside the star. We expect other stars to also form as a nebula contracts into a disk which then feeds the star. These dregs become the planets and smaller bodies. We have observed protoplanetary disks around many young stars. No star older than 25 myrs has a gaseous disk. Hl tau disk, november 2016: at radio wavelengths, this solar system sized disk of dust and gas was found w/gaps, likely due to planet formation. Ingredients for planets in decreasing order of abundance: gas, hydrogen compounds, rocks, and metals. Oxygen is the third most abundant element, and water is the second most abundant molecule, after h2. Inside the frost line, it"s too hot for hydrogen compounds to form ices: terrestrials form primarily out of rocks and metals.
