Bullet cluster

The Bullet Cluster is a system of two merging galaxy clusters. It is notable because it demonstrates that dark matter is a physical reality, distinct from ordinary matter. In this collision, the hot gas (ordinary visible matter) was slowed by drag, while the mass of the clusters, primarily dark matter, was not affected.1

Dark matter constitutes about 26.1% of the universe's matter-energy composition, with ordinary visible matter making up only 0.5%. Dark energy, a repulsive force, is the dominant component at 69.4%. Galaxy clusters are large structures composed of many galaxies, and they themselves are often part of even larger superclusters, which can span up to 200 million light-years.1234