Active galaxy of Markarian 509, Hubble Space Telescope (HST) image. The bright object at the centre of the galaxy is an active galactic nucleus (AGN). AGNs are extremely luminous central regions of galaxies that can outshine all the stars in the rest of the galaxy. AGNs emit radiation across the complete electromagnetic spectrum, from radio waves to gamma-rays, produced by the action of a central supermassive black hole. Image obtained by HST's Wide Field Camera 2 (WFC2).