Star Clusters

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Star Clusters
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Where Do They Come From?

• A cluster is what you get once a parent cloud has
  collapsed and created stars
• All stars begin as part of a cluster

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3 Types of Star Clusters

• Open Cluster
• Association
• Globular Cluster

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Open Cluster

• Ex the Pleiades, Beehive, Hyades
• They are loose, irregular in shape and usually
  found in the plane of the Milky Way
• Contain a few hundred to a few tens of thousands
  of stars

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Open Clusters cont

• They are a few parsecs across
• It will contain stars that lie on all parts of
  the main sequence
• Disperse in a few billion years

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Associations

• Less massive, more extended
• Have no more than a few hundred stars
• May be 10s of parsecs across

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Associations cont

• Tend to contain young stars
• Disperse in a matter of only a few 10s of
  millions of years

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Globular Cluster

• Ex Herculean Cluster
• Have a spherical shape
• Contain hundreds of thousands of stars
• Are over 50 pc across

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• Do not contain main sequence stars greater than
  about 0.8 solar masses
• It is believed that this is because they are old
  (10 billion yrs old) and the big stars have died
  already

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• A is on top, B is on the bottom
• Which type of cluster is A?
• Which type of cluster is B?