APOD: Comet Garradd and Messier 15 (2011 Aug 06)

Comments and questions about the APOD on the main view screen.
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Chris Peterson
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Re: globular clusters

Post by Chris Peterson » Mon Aug 08, 2011 4:28 pm

bosonm wrote:The August 6th APOD showed the Garrad Comet and Messeir 15, a closed globular cluster. My question is: what keeps the cluster so tightly packed? Is there a massive star in the center that acts as a strong gravitational attractor, or could there be a black hole there?
There could be a massive black hole, but it so, it would have little to do with keeping the stars together. A globular cluster is held together by the same thing that keeps a single star together: the mutual gravitational attraction of each of its parts to the rest. In a globular, each star is in orbit around a point that represents a center of mass from its current position. There need be no physical object at that dynamical center of mass.
Chris

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bystander
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Re: globular clusters

Post by bystander » Mon Aug 08, 2011 4:43 pm

bosonm wrote:The August 6th APOD showed the Garrad Comet and Messeir 15, a closed globular cluster. My question is: what keeps the cluster so tightly packed? Is there a massive star in the center that acts as a strong gravitational attractor, or could there be a black hole there?
A good place to start for your answer is the wikipedia article on globular clusters.
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