All the visible matter in space - planets, stars and galaxies - makes up just four percent of the universe. Far more matter is invisible and can only be recognized by the gravity it exerts on its surroundings - thereby helping to hold galaxies together.Astronomers call this 'dark matter'. They want to find out what makes up the mysterious substance that permeates the universe. Particle physicists at CERN hope to use the Large Hadron Collider there to create and study dark matter. And new telescopes are being built to aid the search for dark matter in space.