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Chapter 15 and 16: Discovering Galaxies The Milky Way Galaxy Whenever life gets you down, Mrs. Brown, And things seem hard or tough, And people are stupid, obnoxious or daft, And you feel that you've had quite eno-o-o-o-o-ough... Just remember that you're standing on a planet that's evolving And revolving at nine hundred miles an hour, That's orbiting at nineteen miles a second, so it's reckoned, A sun that is the source of all our power. The sun and you and me and all the stars that we can see Are moving at a million miles a day In an outer spiral arm, at forty thousand miles an hour, Of the galaxy we call the "Milky Way". Our galaxy itself contains a hundred billion stars. It's a hundred thousand light years side to side. It bulges in the middle, sixteen thousand light years thick, But out by us, it's just three thousand light years wide. We're thirty thousand light years from galactic central point. We go 'round every two hundred million years, And our galaxy is only one of millions of billions In this amazing and expanding universe. Galaxies seem to take one of four different appearances SPIRALS Galaxies seem to take one of four different appearances BARRED SPIRALS Edge on Spiral Galaxies seem to take one of four different appearances Type E0 Type E3 ELLIPTICALS Type E6 Galaxies seem to take one of four different appearances IRREGULAR Galaxies that look like merger remnants Galaxy Mergers Mergers cause the shapes of galaxies to change over time. Galaxy Classification A B C D E F Our View of the Milky Way Galaxy Our Milky Way Galaxy? This object that looks like a star must be enormously luminous – because it is 4 billion light years away!! What are Quasars? Quasars get their energy from swallowing up matter in the accretion disk Quasars and other Active Galaxies 90% of a Galaxy is Dark Matter! Measuring the amount of Dark Matter in the Universe: Gravitational Lensing Perfectly Aligned Slightly Misaligned Einstein’s General Theory of Relativity says that light from a distant object gets bent when it passes through a gravitational field of an intervening object. Gravitational lensing Gravitational Lensing: Evidence for dark matter The Birth and Life of Galaxies View of the Early Universe with WMAP (2003) Early Universe showed slight variations in density! Are the density variations the seeds of galaxy formation?? Now the popular choice for galaxy formation! Young Galaxies • smaller • bluer • more irregular • higher star forming rates Galaxies as they appeared more than 10 billion years ago. Galaxies are Grouped in Clusters Now the popular choice for galaxy formation! The Local Group The Local Group The Local Super Cluster Large-Scale Structure in the Universe Superclusters, walls, and voids dominate the large scale structure of the Universe