Images: Observatories at the top of the world

What astronomers are calling a cosmic "train wreck" in the galaxy cluster system known as Abell 520 was revealed when data from NASA's Chandra X-ray Observatory was coupled with images from the Canada-France-Hawaii Telescope and Subaru Telescope atop Mauna Kea. A dark matter core was discovered--filled with gas but without galaxies.

Here's how the Canada-France-Hawaii Telescope site describes the image: "The individual galaxies appear in the CFHT MegaCam visible-light observations (yellow and orange), which also reveal the presence of dark matter (blue) by the subtle distortions of the distant objects. X-rays from Chandra (red) show the hot gas that envelopes the clusters."