Fifth milestone: 605 light years from Earth
Cygnus A, which lies over 700 million light years from Earth, is the brightest radio galaxy in the sky - and one of the first to be discovered in the early 1950s. Its colossal radio jets, which span more than half a milion light years, are produced by its supermassive black hole "engine", which accelerates charged particles close to the speed of light along the galaxy's intense magnetic field lines. The image shown above was taken by the Very Large Array radio telescope in New Mexico.
In 1994 astronomers, using the ultraviolet sensitivity of the Hubble Space Telescope's Faint Object Spectrograph, established that the core of Cygnus A harbours a quasar, powered by its supermassive black hole.
Main image credit: National Radio Astronomy Observatory, C. Carilli