AST 2002 Lecture Notes - Lecture 15: Hydrogen Atom, Solar Mass, Orbital Period
Document Summary
Dusty gas clouds obscure our view because they absorb visible light. This is the interstellar medium that makes new star systems. Stars in the disk all orbit in the same direction with a little up-and-down motion. Orbits of stars in the bulge and halo have random orientations. Star-gas-star cycle: recycles gas from old stars into new star systems. Multiple supernovae create huge hot bubbles that blow out the disk. Gas clouds cooling in the halo can rain back down on disk. Atomic hydrogen (h2) gas forms as hot gas cools, allowing electrons to join with protons. Molecular clouds form next, after gas cools enough to allow atoms to combine into molecules. Gravity forms stars out of the gas in molecular clouds, completing the star gas star cycle. Halo stars- 0. 02-0. 2 % heavy element, only old stars: spheroidal population. Disk stars 2% heavy, stars of all ages, disk stars formed later and kept forming: disk population.
