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Open Star Cluster

General Information

  1. They lie in the plane of the galaxy

  2. They are made of young (newly formed) stars.

  3. They are believed to originate from large cosmic gas/dust clouds in the Milky Way.

  4. They will continue to orbit the galaxy through the disk.

  5. Most open clusters will probably dissipate after a few 100 million to a few billion years since they are only loosely bound by their mutual gravity.

  6. The separation of stars is about 3 light years. In the solar neighborhood stars are 4-5 light years apart.

  7. They contain a few hundred to a few thousand stars.

  8. Star clusters are important to astronomers because they are used to test ideas of stellar evolution. Astronomers are able to do this because all the stars in the cluster are assumed to have formed at the same time.

    a. Theories of stellar evolution are based on computer models. The computer models are based on what we know about stars and the laws of physics. One of the things these models tell us is that different stars age at different rates.

    b. To test their theories, astronomers generate models of stars that would be found in a cluster. They then compare the appearance of this model cluster with observations of a real cluster. If there are significant differences, the astronomers change the model until it matches the real cluster.
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References
Item Updated Notes
-- -- Previously: gave typical age as most clusters “dissipate after a few billion years” – BUT http://messier.seds.org/cluster.html says an “average open cluster” has spread out after several 100 million years, only a few have age counted in billions of years.