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Groups & Clusters of Galaxies

Chandra images provide dramatic evidence of these mega-mergers. Cosmic "weather systems" millions of light years across are observed, as relatively cool 50 million degree Celsius clouds of gas fall into much larger and hotter clouds.

Abell 2142
Chandra image of the galaxy cluster Abell 2142 in X-rays.
It takes a long time to build a galaxy cluster. Exactly how long depends on details such as the amount of dark matter in the universe, whether the dark matter is hot or cold, how fast the universe is expanding, etc. The pressure in the hot gas is an accurate probe of the amount of dark matter in clusters of galaxies. By using this information, and X-ray surveys to count the number of large clusters in the universe, astronomers can test the various theories for the content and evolution of the universe.

Chandra observations of the clouds of hot gas in clusters of galaxies will provide other clues to the origin, evolution and destiny of the universe. Combined X-ray and microwave observations can measure the effect of the cluster gas as it scatters the cosmic microwave background streaming through the cluster from the depths of the universe. The amount of scattering makes it possible to estimate the distance to the cluster. This information can be used to estimate the size and age of the universe.

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