Fourth milestone: 604 light years from the Earth
Centaurus A is a bright galaxy about 13 million light years from Earth. It is the fifth brightest galaxy visible in our skies and one of the closest radio galaxies to our own. The image shown above is a composite of optical, millimetre and X-ray observations. The supermassive black hole at the centre of the galaxy produces strong X-rays, as detected by NASA's Chandra Space Telescope.
Infra-red observations confirm that Centaurus A is devouring a spiral galaxy, causing an intense burst of new stars to be formed. These hot young stars are irradiating clouds of hydrogen gas in the galaxy, producing the characteristic red light - known as H alpha emission - associated with electrons changing energy within hydrogen atoms.
Main image credit: NASA (CXC) and ESO