Photo: "Cosmic Train Wreck" May Derail Theories of Dark Matter

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A composite image combining observations from x-ray and optical telescopes shows the bizarre "cosmic train wreck" of Abell 520, the result of a massive galactic collision.

The bulk of the mass, mostly dark matter, is shown in blue, while hot radiating gas is glowing red and individual galaxies are yellow and orange. Dark matter and galaxies are expected to move in tandem through such crashes, so the presence of dark matter without galaxies, and vice versa, is threatening to rewrite our current understanding of the mysterious substance.

X-ray: NASA/CXC/UVic./A.Mahdavi et al. Optical/Lensing: CFHT/UVic./A.Mahdavi et al.

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