As galaxies speed through gigantic cauldrons, they occasionally jumble the gas and forge it into lop-sided shapes. An example is revealed in this space wallpaper, which is a composite image of the galaxy group NGC 5044, the brightest group in X-rays in the entire sky. Galaxies are social beasts that are mostly found in groups or clusters — large assemblies of galaxies that are permeated by even larger amounts of diffuse gas. With temperatures of 10 million degrees or more, the gas in galaxy groups and clusters is hot enough to shine brightly in X-rays and be detected by ESA’s XMM-Newton X-ray observatory.
(Image: © E. O’Sullivan and ESA)