Globular Cluster NGC 6388

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This image from the Hubble Space Telescope shows NGC 6388, a dynamically middle-aged globular cluster in the Milky Way. While the cluster formed in the distant past (like all globular clusters, it is over ten billion years old), a study of the distribution of bright blue stars within the cluster shows that it has aged at a moderate speed, and its heaviest stars are in the process of migrating to the center. Globular clusters are spherical collections of stars, tightly bound to each other by their mutual gravity. Relics of the early years of the Universe, with ages of typically 12-13 billion years (the Big Bang took place 13.7 billion years ago), there are roughly 150 globular clusters in the Milky Way and they contain many of our galaxy's oldest stars. A new study using Hubble data has discovered that globular clusters of the same age can have dramatically different distributions of blue straggler stars within them, suggesting that clusters can age at substantially different rates.
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Image Credit: NASA, ESA, F. Ferraro (University of Bologna)
Image enhancement: Jean-Baptiste Faure