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Compact Cosmos

9 8 GALAXYTYPES whorls and wisps Roughly threequarters of visible galaxies are,like our own,spirals, flattened disks with a central bulge. Young stars,along with gas and dust, hang in the disk. Older stars prefer the bulge or amble the surrounding spherical haloin groups. Spirals come in normal and barred varieties,depending on their centers. Mainly populated by older stars,the less structured elliptical galaxies are roughly spherical with differing degrees of flattening. In between,lenticular galaxies are a heady mix of both types. Harder to fathom are irregular galaxies, with shapes sculpted by gravitation or collision lower opposite. Most are star formation hotbeds,with dense clouds of gas amidst crowds of young stars. Dark and difficult to detect, surveys suggest that dwarf and low surface brightness galaxies perhaps outnumber all the rest. For ease, galaxies are classified by the Hubble Sequence. Rather optimistically designed to explain galactic evolution, it groups by shapeand features below. Our own Milky Waygalaxy is type Sb or Sc,but with an additional slight bar on the bulge.
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