... Galaxies . ... For the first time dark matter may have been observed interacting with other dark matter in a way other than through the force of gravity. ... In this study, the researchers observed the four colliding galaxies and found that one dark matter clump appeared to be lagging behind the galaxy it surrounds. ... Lead author Richard Massey at Durham University, explains: тАЬ We used to think that dark matter just sits around, minding its own business, except for its gravitational pull. ...