Galaxies - Research Article from Macmillan Science Library: Space Sciences

This encyclopedia article consists of approximately 9 pages of information about Galaxies.
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Galaxies

Galaxies are collections of stars, gas, and dust, combined with some unknown form of dark matter, all bound together by gravity. The visible parts come in a variety of sizes, ranging from a few thousand light years with a billion stars, to 100,000 light-years with a trillion stars. Our own Milky Way galaxy contains about 200 billion stars.

Types of Galaxies

Elliptical Galaxies.

Elliptical galaxies are three-dimensional objects that range from spheres to elongated spheroids like footballs. Some may have developed from slowly rotating hydrogen clouds that formed stars in their first billion years. Others may have formed from the merger of two or more smaller galaxies. Most ellipticals have very little gas left that can form new stars, although in some there is a small amount of star formation within gas acquired during recent mergers with other galaxies.

Spiral Galaxies.

Spiral galaxies, which include the Milky Way, formed from...

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This section contains 2,401 words
(approx. 9 pages at 300 words per page)
Buy the Galaxies Encyclopedia Article
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Macmillan Science Library: Space Sciences
Galaxies from Macmillan Science Library: Space Sciences. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.
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