Hubble Space TelescopePseudo-color image of the ultra-diffuse galaxy FCC 224.The above image might not look unusual, but it poses an interesting mystery for astronomers. Captured by the Hubble Space Telescope, it is an image of an ultra-diffuse galaxy (UDG) known as FCC 224. Unlike regular dwarf galaxies such as the Magellanic Clouds, these galaxies have an unusually low surface brightness for a galaxy of their size. This usually means they contain lots of dark matter. The gravity of the dark...
