Interacting quasar. Hubble space telescope (HST) optical image of a quasar (bright, at centre) interacting with a companion galaxy. The galaxy's core is at lower centre. Around the quasar & companion are swirling wisps of gas. Another galaxy, possibly beginning its interaction with the quasar, is at centre left. Quasars are black holes at the centre of galaxies. The gravitational field of the black hole drags in matter, including whole stars. This matter releases radiation as it falls towards the hole. Image of quasar PG 1012+008; it is 1.4 billion light-years away from Earth and 35,000 light-years from its companion.