Lecture 23 - Active and Normal Galaxies

Lecture 23 - Active and Normal Galaxies - Normal and Active...

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Normal and Active Galaxies ASTRONOMY 3 Lesson 23 1 Ground-based image of the Andromeda Galaxy (M31) - see http://hubblesite.org/ newscenter/archive/releases/galaxy/spiral/2005/26/image/c/
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NATURE of the Universe Review of Lesson 22 • The spiral arms of the Milky Way are caused by density waves. This results in density enhancements of the interstellar medium and the formation of stars • The total mass of the Milky Way is estimate to 600 billion times the mass of the Sun. At least 2/3 of the material making up the Milky Way seems to be in the form of “dark matter”. • The center of the Milky Way houses a supermassive black hole with about 3.7 million times the mass of the Sun. Review: Milky Way II 2
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NATURE of the Universe Questions from Lesson 22 Astronomy - Normal & Active Galaxies Think about (questions from Lesson 22): • Are all galaxies spiral galaxies? • Which are the most nearby galaxies? 3
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• Types of galaxies (Ch. 15.1) • The Local Group of galaxies (Ch 15.2) • Hubble’s law (Ch 15.3) NATURE of the Universe Today’s Topics Astronomy - Normal & Active Galaxies Today’s Topics: 4
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5 Astronomers classify galaxies based on their morphology. Some galaxies are disk galaxies with spiral arms, while others have a more uniform 3 dimensional distribution of stars. Still others are irregular in shape.
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NATURE of the Universe Types of galaxies Astronomy - Normal & Active Galaxies In the late 1920s, Edwin P. Hubble grouped galaxies into 3 major types elliptical galaxies spiral galaxies irregular galaxies Elliptical Irregular Spiral 6
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NATURE of the Universe Types of galaxies Astronomy - Normal & Active Galaxies Elliptical galaxies are subdivided further according to their degree of ellipticity from E0 to E7. M87: E0 M32: E2 M59: E5 7
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NATURE of the Universe Types of galaxies Astronomy - Normal & Active Galaxies Elliptical galaxies have no spiral arms and no disk have between less than 1 million stars (dwarf elliptical galaxies) to more than 1 trillion stars (giant elliptical galaxies) contain little cool gas and dust, and have no present or recent star formation often have extended halos of hot gas seen in X-ray observations Main properties of elliptical galaxies The size of the Milky Way in comparison! 8
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Types of galaxies Astronomy - Normal & Active Galaxies Spiral galaxies are arranged according to the “tightness” of their spiral arms and the size of the central bulge: Sa galaxies have larger bulge and tightly wound spiral arms Sb galaxies are intermediate between Sa and Sc Sc galaxies have a small bulge and loosely wound arms NGC 2775: Sa M81: Sb M101: Sc more bulge more disk More disk means more star formation! 9
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Lecture 23 - Active and Normal Galaxies - Normal and Active...

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