Astronomers are still making new discoveries about the shape of the Milky Way. For instance, maps of gas flow near the centre of the galaxy first suggested the influence of a large bar of stars running across the bulge in the 1960s, but this bar was only confirmed using infrared observations in 2005. The bar is thought to create an alignment among the orbits of objects further out, producing the ‘density wave’ effect that generates the spiral arms.