Star Clusters

What is the difference between a large star cluster and a small galaxy?

Astronomers have been trying to answer this question for many years. Omega Centauri, for example, contains several million stars, as does 47 Tucanae. Many dwarf galaxies have comparable numbers of stars, so it is not perfectly clear where a “star cluster” ends and a “galaxy” begins, when it comes to classifying stellar collections of this size. Differences with regard to diameters, or perhaps non-baryonic dark matter content, may eventually help astronomers find a definitive distinction between these two kinds of objects.


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