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Biggest bang since the Big Bang

So big, in fact, that at first scientists didn’t believe it.

the largest structures in the Universe held together by gravity
Galaxy clusters, the largest structures in the Universe held together by gravity, contain thousands of individual galaxies, dark matter and hot gas. Credit: X-ray: NASA/CXC/Naval Research Lab/Giacintucci, S.; XMM:ESA/XMM; Radio: NCRA/TIFR/GMRTN; Infrared: 2MASS/UMass/IPAC-Caltech/NASA/NSF