MARK GARLICK / SCIENCE PHOTO LIBRARY MARK GARLICK / SCIENCE PHOTO LIBRARY
Globular cluster. Artwork of a globular cluster of stars with the anomalous, bright blue stars known as blue stragglers (lower right and upper left). Globular clusters are roughly spherical, dense clusters of hundreds of thousands to millions of stars. These old stars are thought to have been formed from the original material of the Galaxy, and their globular clusters form a spherical halo extending outside the Galactic disc where the open clusters and most of the Galaxy's stars are found. Blue straggler stars, found in globular clusters or old open clusters, are anomalous because their brightness and blue colour mark them out from the normal processes of stellar evolution.
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