Star clusters are gravitationally bound grouping of stars, from a few thousand to many millions. Clusters in other galaxies are too distant to image effectively, so all the images seen here are clusters within or around our own Milky Way. Clusters are grouped into two major categories, and have very different origins. Globular clusters contain hundreds of thousands to millions of stars that are tightly bound, and which are found outside the edges of galaxies. Open clusters contain hundreds of stars, which are loosely bound, and are the slowly dispersing remnants of star forming regions.
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