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What is the overall structure of the Galaxy?

Galaxy overall structure
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What is the overall structure of the Galaxy?

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The Milky Way is a spiral galaxy which consists of a relatively thin disk of stars arranged in a spiral pattern. At the center of the pattern is a roughly spherical but elongated bulge. Completely enveloping this disk is a vast spherical component called the halo. It is in this halo that most of the dark matter in the Galaxy resides. The disk rotates and at the distance of the Sun from the center of the Galaxy (roughly halfway along a radius of the disk) it is spinning at approximately 220 kilometers per second. The halo does not have an overall rotation. Instead, the orbits of stars in the halo about the center of the Galaxy are randomly distributed and usually highly elliptical. These orbits dictate that the stars in the halo move very rapidly, some as fast as hundreds of kilometers per second. For a reference of scale, the Sun lies approximately 26,000 light years from the center of the Galaxy and the halo may be as large as 150,000 light years in radius.

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