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Loading contentA gravitationally bound collection of hundreds to thousands of galaxies — the largest such structures.
Galaxy clusters contain hundreds to thousands of galaxies, vast clouds of hot X-ray gas, and dominant dark-matter halos. They act as cosmic laboratories and gravitational lenses, and their abundance over time probes cosmology.
Facts on this topic will be cited from these primary and reference sources.
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.
Southern-hemisphere observatory data and imagery (VLT, ALMA partner).