Today's What Is series topic is a galaxy. What is a galaxy? I previously discussed a star, and a galaxy is a collection of up to a trillion stars that are gravitationally bound together and also often include a large collection of gas and dust. Galaxies vary in shape and size. There are spiral galaxies, of which the Milky Way Galaxy (our galaxy) is one. There are elliptical galaxies that contain less gas and dust and more older stars. There are also irregular galaxies that are typically smaller in size and are, as the name suggests, irregularly shaped.
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| The Whirlpool Galaxy taken by NASA and the European Space Agency |
The Whirlpool Galaxy, shown above, is a great example of a spiral galaxy with arms spiraling around in a circular shape. Smaller galaxies can contain a few hundred million stars and larger galaxies can contain up to a trillion stars. The Milky Way Galaxy is estimated to have 200-400 billion stars. There are also galaxies possibly made entirely, or mostly, of dark matter with few, if any stars. These are a still a bit unknown at this time, but there is some evidence they exist.
There is much going on in a galaxy that will eventually be covered in this What Is series, but I'll keep today's post simple. A galaxy is a collection of gas and dust, with a few hundred million to a trillion stars. The gas and dust can collect together to make new stars. Galaxies with less gas and dust are done making stars or suggest stellar formation is coming to an end soon.
With billions of estimated galaxies in the Universe and billions of stars in each galaxy, there are billions and billions of solar systems potentially harboring life. Somewhere out there I have to think there must be other intelligent life.
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