When you look up at night, you see myriads of stars spread across the sky. When astronomers look into the deepest reaches of the universe with powerful telescopes, they see myriads of galaxies, organized into large clusters and other structures. This might lead you to believe that the universe is composed mainly of galaxies, stars, gas and dust – things that you can see. However, most astronomers believe that visible matter makes up only a small fraction of the mass of the universe. The majority of the universe is made of stuff we can’t see – so-called dark matter.
