ESA’s XMM-Newton observatory has turned up hot gaseous halos around several spiral galaxies. These ghostly veils have been seen surrounding “starburst galaxies”, which are going through a tremendous amount of star formation – but not around the more common kinds of galaxies. Unlike a starburst galaxies, which concentrates their halos, regular galaxies will have simmering star formation stretching across them entirely. These halos can contain up to 10 million solar masses of gas.