Illustration showing light from a distant quasar being altered by a massive foreground galaxy and tiny dark matter clumps before reaching the Hubble Space Telescope. This warping and magnifying effect, known as gravitational lensing, produces the four distorted images (centre) of the quasar shown. Galaxies are embedded within dark matter clumps that bend light travelling from the quasar to Earth. Dark matter clumps are structures formed from cold matter particles (slow moving particles). These clumps can change the position and brightness of the distorted quasar images. Using images taken by the Hubble Space Telescope, astronomers were able to work out the mass of these tiny dark matter concentrations, by comparing predictions of how the quasar would look without the dark matter clumps to the distorted images.