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About Galaxies in Space

The Milky Way Galaxy in which we live is not alone in the universe; around 100 billion galaxies exist. A galaxy is a collection of stars, dust and gas, with the average galaxy containing billions of stars. One galaxy may contain a million solar systems. Some galaxies have smaller galaxies within close proximity, called satellite galaxies. The closest galaxy to the Milky Way is called the Magellanic Clouds; the furthest known galaxy from us is 14 billion light years away. Some galaxies occur alone, while others occur in pairs or larger associations known as groups, clusters and superclusters.

Size
- Galaxies vary in size considerably. GR-8, the smallest galaxy in the known universe, is only 1,000 light years across. Meanwhile, 3C-236, the largest galaxy in the Universe, is an elliptical galaxy that measures 18 million light years from end to end. A typicial galaxy measures about 100,000 light years across, with a nucleus made up of older stars.
Spiral Galaxies
- Spiral galaxies are shaped like a flat disk with a dense center and "spiraling" arms. The galaxy's stars, planets and dust orbit the the dense galactic center. They contain a number of blue, younger stars. The Milky Way is an example of a spiral galaxy. Some spiral galaxies are given colorful descriptions based on their shape, such as pinwheel galaxies and sombrero galaxies.
Elliptical Galaxies
- Elliptical galaxies are not round but stretch further along one axis than the other. They generally contain a number of red stars that are much older than stars found in the typical spiral galaxy. While their stars orbit the galactic center, just as in spiral galaxies, they do so in more varied paths. Elliptical galaxies can have as many as a trillion stars, but not much else in terms of interstellar matter such as dust. The largest galaxies in the universe are elliptical galaxies; they stretch as much as 2 million light years across.
Irregular Galaxies
- Irregular galaxies are so named because they lack a distinct form. In most cases, this is because of the gravitational influence of nearby galaxies. Irregular galaxies have unusual shapes that disqualify them from being labeled either spiral or elliptical.

Astronomy