3.4 billion light-years

This image shows the galaxy cluster known as the "Bullet Cluster". This system was formed when two large groups of galaxies collided, the most energetic event known in the Universe since the Big Bang. Data from the Hubble Space Telescope and visible light telescopes on the ground show how dark matter (blue) has separated from "normal" matter in the form of hot gas (pink) detected by the Chandra X-ray Observatory. This is direct evidence that dark matter exists.

Credit: X-ray: M.Markevitch for NASA / CXC / CfA and visible light by D.Clowe for NASA / STScI; Magellan / U.Arizona and ESO.

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