AST 101 Lecture Notes - Lecture 15: Not Proven, Before Present, Main Sequence
21 Jul 2016
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Chapter 20 - galaxies and the foundation of modern. Spiral arms are density waves of stars and the gas, like traffic jams. Squeezed gas in spiral arms can collapse by its own gravity and form stars. Red dots are star forming regions (emission from ionized gas, which is the gas ionized by photons from young massive stars) Motions of stars in this galaxy are like the ones in a bulge. It has much less stars compared to spiral or elliptical galaxies. Galaxy is an ensemble of ~100 billion stars of both high and low masses. > as stellar population gets older, it becomes more red-yellow since high mass stars die and low mass stars remain. One of our deepest images of the universe show a great variety of galaxies, some of them billions of light-years away. A galaxy"s age, its distance, and the age of the universe are all closely related.
