Active Galaxies

Some galaxies show evidence for the generation of enormous amounts of energy from the vicinity of their nucleus. The adjacent image shows a galaxy named NGC4261 that has gigantic radio frequency jets emerging from its nucleus (left side). The right side shows a Hubble Space Telescope image of the central region of the galaxy where an enormous black hole is suspected to exist. These active galaxies are often strong radio emitters and often show complex lobe structure extending for millions of light years. Other galaxies have such energetic nuclei that we only see the bright nucleus and not the underlying galaxy; we call these objects quasars (quasi-stellar objects).

The presence of black holes at the centres of these objects is thought necessary by many astronomers to explain their nature. Because they are the brightest objects known in the universe it is not surprising that quasars are the objects that have been traced out furthest from us. The furthest known are so far away that the light we see coming from them must have originated when the Universe was only one tenth of its present age.