File:An Intergalactic Heavyweight.jpg
This image was taken by the Wide Field Imager (WFI) camera on the MPG/ESO 2.2-metre telescope, located at the La Silla Observatory in Chile. Using data from the WFI and from the NASA/ESA Hubble Space Telescope, in 2008 astronomers were able to precisely map the distribution of dark matter in the supercluster, showing that the clusters and individual galaxies which comprise the super-structure reside within vast clumps of dark matter. To do this, astronomers looked at how the light from 60 000 faraway galaxies located behind the supercluster was being distorted by the gravitational influence of the dark matter it contains, thus revealing its distribution. The mass of the four main dark matter clumps of Abell 901/902 is thought to be around ten trillion times that of the Sun.
The observations shown here are part of the COMBO-17 survey, a survey of the sky undertaken in 17 different optical filters using the WFI camera. The COMBO-17 project has so far found over 25 000 galaxies.