AST- 105 1st EditionLecture 20Outline of Last LectureI. SupernovaII. Neutron StarsIII. Pulsar ModelOutline of Current Lecture I. The Milky Way GalaxyCurrent Lecture I. The Milky Way Galaxya. The Milky Way Galaxy- our galaxy; a large spiral galaxy containing approximately 10^11 stars. 1. Our Sun is located in the disk.2. Milky Way band in the sky = disk of our galaxy1. We see more stars looking through the disk than out of the disk, since path through the disk is longer.b. The Milky Way in Infrared1. Dust blocks view in visible light, so we cannot see long distance through the disk in visible light.1. Therefore the disk is best observed in Infrared.c. Structure of the Milky Way Galaxy1. Disk- frisbee shaped1. Contains stars, gas, and dust in a spiral pattern2. Young and old stars3. 100,000 ly in diameter4. 2,000 ly thick5. Sun located about midway between center and edge6. Recent studies in infrared light indicate a bar at the center.2. Motions in the disk1. Stars and gas clouds in disk follow nearly circular orbits (like planets in solar system)2. Orbital period of Sun:1. 2 x 10^8 yr3. 25 orbits have been completed by the Sun.3. Evolution in the disk1. Contains gas and dust clouds2. Star formation is ongoing3. Each stellar generation adds “metal” (elements heavier than H andHe) to interstellar gas, from supernova explosions.4. Young stars have a higher metal content in their atmospheres thanold stars since young stars form from enriched
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