the first signs of dark matter interacting with a force other than gravity may have been found .
until now it was thought that dark matter did not interact with anything other than gravity , earning it its ` dark ' moniker and making its detection incredibly difficult .
but the discovery of a ` clump ' lagging behind a galaxy suggests it may not be as oblivious to our universe as we thought .
in this hubble image , the lagging clump can be seen on the left of the central cluster .