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lecture_tan30 - Key Concepts Lecture 30 Galaxies Elliptical...

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Key Concepts: Lecture 30: Galaxies Galaxy Types: Spirals, Ellipticals, Irregulars, Dwarfs Spiral Density Waves The Classification of Galaxies Galaxies can be classified by how they appear on the sky How flattened the spheroid is How prominent the disk and spiral arms are If there is a bar Hubble devised what he thought may be an evolutionary sequence Elliptical Galaxies Only a smooth spheroidal component Hubble class subdivides them E0 - circular E7 - most elongated No prominent disk Composed of old reddish stars Little dust, gas or ongoing star formation M87 - E0 E7 Spiral Galaxies Have disk with two or more arms Bulge is old and red Disk has gas and star formation Hubble sequence (Sa, Sb, Sc) size of nuclear bulge vs. disk tightness of spiral arms Sa - tightest pattern & large bulge Sc - open pattern & smallest bulge S0 or lenticular Have disk but no arms Sb Sc
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M83 classed as SBb bar NGC 4565 - Edge on Sb Sombrero Galaxy Sa M84 S0 What are Spiral Arms?
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