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Lecture 11: Galaxies and Their Nuclei. The Hubble Deep Field. Eye on a Dime. The Hubble Ultradeep Field. Brief Review of Galaxy Structure. Disks Prominent feature in spiral galaxies (like Milky Way) Stars in nearly circular orbits Analogies: Solar System, accretion disk Bulges
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Brief Review of Galaxy Structure • Disks • Prominent feature in spiral galaxies (like Milky Way) • Stars in nearly circular orbits • Analogies: Solar System, accretion disk • Bulges • Coexist with disks in spirals (central bulge, halo) • Elliptical galaxies: whole galaxy is bulge • Stars in random orbits
Galaxy Disks Artist’s Impression of Our Galaxy’s Disk Disk of the Galaxy NGC 1672
Galaxy Bulges Sombrero Galaxy – Note the Large Bulge
Main Contents of Galaxies • Dark Matter(~80% of halo, smaller proportion of disk) • Stars • Large galaxy has 100 billion stars (range 107-1012 stars) • “Collisionless”, interact by gravitational forces • Gas • > 10% of star mass • “Dissipative”, tends to form clouds, sink to center • Can fall in from outside or escape in wind • Dust • About 1% of gas mass, follows gas motion • Obscuration
The Radio Source Sgr A* The red dot at the center is Sgr A*