Illustration of the Milky Way galaxy with a halo of gas. The Milky Way is shown as a dark spiral in the centre of the image surrounded by the halo of gas. The gas is shown in three different shades, emerald, yellow and green each representing gas of a different temperature. A halo is a vast region of gas, stars and invisible dark matter surrounding a galaxy. It is a key component of a galaxy, connecting it to wider intergalactic space, and is thus thought to play an important role in galactic evolution. Data from ESA?檚 XMM-Newton X-ray space observatory shows the Milky Way?檚 halo contains three different components of hot gas, the first time multiple gas components have been observed in any galaxy halo.