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Intro

A spiral Galaxy is a type of galaxy distinguished by it's shape of multiple spiral arms coming inwards into a central bulge.The bulges almost always contain a supermassive black hole that is billions of solar masses in size. Some of the largest galaxies that we know of are spirals . Our galaxy is a spiral along with larger Andromeda Galaxy.In the outer boundary of a spiral Galaxy there is a halo of older stars.

Bulge

The bulge contains old , population 2 stars and resembles an elliptical galaxy. Many of the stars in the bulge are red giants . Occasionally a "starburst" event ,a flood of incoming matter causing a burst of star formation , will occur.

Spiral Arms

The arms rotate around the bulge and are made up of young population 1 stars . Open Star Clusters are common in the disc and are made up of up to 10000 stars. We live in the Arms of a spiral Galaxy

Halo

The halo of matter at the edge of a spiral Galaxy is made up of old population 2 stars in massive globular clusters that contain up to 10000000 stars

References

"Spiral Galaxy." Wikipedia. 16 Aug. 2007 <http://en.wikipedia.org/wiki/Spiral_galaxy>.