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The Question

(Submitted February 15, 1998)

What different types of galaxies are there? What are their similarities and differences?

The Answer

There are indeed different types of galaxies. The main types are spiral galaxies (like our own MilkyWay), elliptical galaxies and irregular galaxies. An irregular galaxy has an undefined shape and has lots of young stars, dust and gas. A spiral galaxy is shaped like a disk, usually with a bulge in the center and with arms that spiral outwards as the galaxy rotates. Spiral galaxies tend to contain more middle-aged stars along with clouds of gas and dust. Elliptical galaxies contain older stars and very little gas and dust. They can be different shapes ranging from round, to flattened, elongated spheres.

J. Allie Cliffe
for Ask an Astrophysicist

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