Galaxy clusters are large structures in the universe that consist of hundreds to thousands of galaxies bound together by gravity. They are among the largest known gravitationally-bound structures in the universe and contain not only galaxies but also vast amounts of hot gas, dark matter, and, in some cases, dark energy. Here are some key features of galaxy clusters: 1. **Composition**: A typical galaxy cluster contains a mixture of galaxies, hot intracluster gas (which emits X-rays), and dark matter.
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