Normal Galaxies - Hubble Classification
4 Types:
•Spirals
–flattened galactic disk with dust, gas, stars (spiral arms) + central bulge with dense nucleus + extended halo of faint old stars
•Barred Spirals
–elongated bar of stars, dust, gas crosses center; spiral arms “originate” from bar ends not bulge 
•Ellipticals
–older spheroidal star system no spiral arms, no young stars, little gas, dust
•Irregulars
–irregular shape, lots of gas, young blue stars
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•Elliptical galaxies are most massive – often seen at
•center of dense galaxy clusters
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Andromeda
NGC 2997
NGC 4565