lecture_5 - G a l a x i e s Galaxies are self-gravitating...

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Unformatted text preview: G a l a x i e s Galaxies are self-gravitating systems containing billions of stars and having diameters of 1025 kpc (1 kpc = 1000 pc = 3260 lt.-yr.). The observed universe has billions of galaxies. We live in a Galaxy known as the Milky Way. Galaxies dont exist randomly in space, but tend to cluster. Cluster sizes range from a few dozen members, as in our Local Group, to 10,000 like the Virgo Cluster. Galaxies began forming 13 Gyr ago when the universe was 1 Gyr old. Quasars may be young galaxies Galaxies are believed to consume neighboring galaxies. The Milky Way has consumed several nearby dwarf galaxies; the Magellanic Clouds will be consumed in the near future. Galaxies are classified according to appearance. Its unknown if galaxies evolved from one class into another. Our galaxy is a barred spiral. S . H a r r is Lattimer, AST 248, Lecture 5 p.1/14 S t r u c t u r e o f t h e M i l k y W a y The Milky Way is a barred spiral galaxy with 200-400 billion stars and 6 10 11 M of stars and gas and 6 30 10 11 M of dark matter. Major components include the nucleus (bulge), halo and disk (spiral arms.) The galactic center contains a supermassive black hole of 3 10 6 M called Sagittarius A. Most galaxies are believed to have black holes at their centers. The galaxys nucleus is bar-shaped and about 27,000 lt.-yrs. long, and is composed of ancient red stars. The galaxys disk contains molecular clouds, young stars, and galactic clusters, largely concentrated in a ring around the bar and in 4 major spiral arms. Most current star formation occurs here. The disk diameter is about 100,000 lt.-yrs. Spiral arms are logarithmic spirals ( r = ae b ), just like the spirals in a nautilus shell or a hurricane. The Sun is located at the inner rim of the Orion Arm, 25,000 lt.-yrs. from the galactic center. The galactic halo is a spheroid of old stars and globular clusters with a diameter estimated at 200,000 lt.-yrs. The galaxys dark matter is uniformly distribued within the halo. c a s s w w w .u c s d .e d u /p u b l ic / tu to r ia l /M W .h tm l Lattimer, AST 248, Lecture 5 p.2/14 www.anzwers.org/free/universe/milkyway.html Lattimer,AST248,Lecture5p.3/14 C o m p o n e n t s o f t h e G a l a x y N A S A /E S A /A U R A /C a l te c h Pleiades S p a c e T e le s c o p e S c ie n c e In s t i tu te M 80 H . Y a n g & J . H e s te r , N A S A NGC 604 Many stars in the disk are in open clusters....
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This note was uploaded on 01/25/2012 for the course AST 248 taught by Professor Walter during the Spring '08 term at SUNY Stony Brook.

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lecture_5 - G a l a x i e s Galaxies are self-gravitating...

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