This image of the galaxy cluster Abell 520 — 2.4 billion light-years away — may challenge some of our basic theories about Dark Matter. It is overlaid with false-color maps showing concentrations of starlight (orange), hot gas (green) and mass (blue). The mass is mostly Dark Matter. M.J. Jee and A. Mahdavi/NASA/ESA/CFHT/CXO hide caption

itoggle caption M.J. Jee and A. Mahdavi/NASA/ESA/CFHT/CXO