Spirals - Spirals The Whirlpool Galaxy (on left), an...

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Spirals The Whirlpool Galaxy (on left), an example of an unbarred spiral galaxy. Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. Extending outward from the bulge are relatively bright arms. In the Hubble classification scheme, spiral galaxies are listed as type S , followed by a letter ( a , b , or c ) that indicates the degree of tightness of the spiral arms and the size of the central bulge. An Sa galaxy has tightly wound, poorly defined arms and possesses a relatively large core region. At the other extreme, an Sc galaxy has open, well-defined arms and a small core region. [51] A galaxy with poorly defined arms is sometimes referred to as a flocculent spiral galaxy ; in contrast to the grand design spiral galaxy that has prominent and well-defined spiral arms. [52] In spiral galaxies, the spiral arms do have the shape of approximate logarithmic spirals , a pattern that can be theoretically shown to result from a disturbance in a uniformly rotating mass of stars. Like the stars, the spiral arms rotate around the center, but they do so with constant
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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Spirals - Spirals The Whirlpool Galaxy (on left), an...

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