Spiral arm
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Galaxy.m74.arp.750pix.jpg
Galaxy.m74.arp.750pix.jpg
A spiral galaxy presents a face-on view of its spiral arms.
Spiral arms are regions of stars that extend from the center of spiral and barred spiral galaxies. These long, thin regions resemble a spiral and thus give spiral galaxies their name.
The existence of spiral arms has puzzled scientists. The stars on the outermost edge of the galaxy would move faster than those near the center as the galaxy rotates. See discussion in spiral galaxy for further information.