Fact Sheet
Cosmic Bullets
This giant cluster of galaxies and hot gas, known as the Bullet Cluster, provides strong evidence of dark matter, a mysterious form of matter that produces no detectable energy but that exerts a strong gravitational influence on the visible matter around it. Two big groups of galaxies have passed through each other relatively undisturbed. Gas in the galaxies has rammed together and remained in the center of the cluster. The gas has heated to millions of degrees, producing X-rays (shown in red). The gravity of the galaxies "bends" the light of galaxies behind it. From this effect, astronomers calculate that the cluster must contain enormous amounts of dark matter (the densest concentrations of dark matter are shown in blue). Like the visible galaxies, the clouds of dark matter around them have passed through each other with no effect. [NASA/CXC/CfA/M.Markevitch; STScI/Magellan/U.Arizona/D.Clowe; ESO WFI]
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