What is a galaxy cluster?
Quick Answer
A galaxy cluster is a large group of galaxies bound together by gravity. It can contain hundreds or thousands of galaxies plus hot gas and dark matter.
The Full Story
Galaxy clusters are some of the largest known structures held together by gravity. They include galaxies, hot intracluster gas, and large amounts of dark matter. The gas between galaxies can be so hot that it emits X-rays. Clusters grow by merging with other clusters and by pulling in nearby galaxies. Studying them helps astronomers understand large-scale structure in the universe and how matter is distributed across cosmic time.
Key Facts
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"The universe’s biggest city blocks are packed with galaxies, gas, and dark matter"
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