Cosmology - the study of the universe on its largest scale - is the most challenging area in astronomy. It is also astronomy's newest field, dating from just over a century ago. Until then, we were unaware of the extent of the universe around us. First came the discovery that our Sun is part of a Galaxy of 200 billion stars, and then that our Galaxy is just one of a hundred billion galaxies in the universe. Next came the finding that all the galaxies are rushing away from one another, showing that our cosmos was once a more crowded place. Now astronomers know that the universe began some 13 billion years ago in the Big Bang - but the future is still unknown.
A small number of galaxies are different from all the rest, pouring out huge amounts of energy from a tiny region at their centers not much bigger than the solar system. These so-called active galaxies, which include quasars, radio galaxies, Seyfert galaxies, and blazars, are all members of the same family of objects. Though they are related, what we see depends on how far away the galaxy is and the angle at which we are viewing it.
All active galaxies share many common features, but only radio galaxies show all aspects of these complex structures. From a distance, the most obvious features are the radio-emitting jets emerging from either side of the galaxy and billowing out into vast clouds. Closer in, at the heart of the galaxy, lies a doughnut-shaped ring of dust and gas, heated until it glows brilliantly. At the heart of each one is a supermassive black hole that generates enough power to outshine the Sun by a trillion times!
