“Every single time you make a merger, somebody is losing his identity. And saying something different is just rubbish.” -Carlos Ghosn

A galaxy cluster is the largest individual bound structure in the Universe, containing anywhere from dozens to thousands of times the mass of our Milky Way. Yet as the cosmic web grows and evolves, many such clusters merge together, creating the largest cosmic trainwrecks in the Universe.

Image credit: NASA / STScI, of cluster MACS J0717.5+3745 in the optical, courtesy of Hubble Frontier Fields.

Image credit: NASA / STScI, of cluster MACS J0717.5+3745 in the optical, courtesy of Hubble Frontier Fields.

While very little evidence of a catastrophe is visible in the optical, the X-ray and radio emissions from these collisions tell a deep and varied story, and enable astronomers to reconstruct not only what physical processes are at play, but to understand how our large-scale structure evolves over billions of years.

Image credit: NASA/CXC/SAO/G.Ogrean et al., of galaxy cluster MACS J0717.5+3745 in the X-ray, courtesy of Chandra.

Image credit: NASA/CXC/SAO/G.Ogrean et al., of galaxy cluster MACS J0717.5+3745 in the X-ray, courtesy of Chandra.

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