Energetic X-rays (pink) are emitted by hot normal matter that has piled up where two clusters of galaxies have collided. The dark matter (blue) has mysteriously passed through the crash undisturbed.Credit:
X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.