Macs J0025.4-1222 in 60 Seconds Plus (09-04-2008)
Two galaxy clusters, each a quadrillion times the mass of the Sun, collided to form the system formally known as Macs J0025.4-1222.

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--  MACS J0025.4-1222

Giants of the Universe Probe Cosmic Questions (11-30-2006)
Clusters of galaxies are the largest structures in the Universe that are held together by gravity. Because of their immense size and mass, galaxy clusters are extremely useful as tools to probe a variety of questions about the Universe as a whole as well as properties of the clusters themselves.

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--  Groups & Clusters of Galaxies