Dark matter map. Computer model of a dark matter (red) map in part of the universe a billion light years long, the first time the invisible dark matter between visible objects has been mapped. Its position has been inferred from the effect its gravitational pull has on the light (yellow lines) from galaxies (blue). Without dark matter, these lines would be straight. The mass of the visible universe is only about a tenth of that calculated from observations, and dark matter is thought to constitute the missing mass. This work was done by Yannick Mellier and his team from the Paris Astrophysics Institute, France, using the Canada- France-Hawaii Telescope on Mauna Kea, Hawaii, USA.