Astronomers have found the strongest evidence so far that dark matter exists.
Doug Clowe from the University of Arizona in Tuscon and his collegaues have spied a cluster of galaxies in which the centre of mass is shifted to the side of the bulk of observable material, in a relatively empty patch of sky. This implies that there must be some 'dark matter' filling up the empty space.
Decades ago, researchers found from watching distant galaxies that their gravitational properties cannot be explained by the visible material: they posited that some 'dark matter' must make up the difference. Dark matter is thought to account for roughly a third of the mass in the Universe, although it has never been directly detected.