Active galaxies are unique and release enormous amounts of
energy. First discovered in the forties, the Seyfert Galaxies have a
bright core. Quasars are especially bright distant galaxies that
release as much energy as a thousand galaxies like ours. Radio
galaxies emit a huge amount of energy in the form of radio waves. The
intense activity is probably due to black holes, bodies so massive
and dense that near stars are trapped and spiral inward at high
speed, breaking up and releasing energy before disappearing into the
black hole. The star debris and gases orbiting the black hole form a
bright disk called an accretion disk. Active galaxies shine for only
a few million years then when deprived of fuel the accretion disk
disappears and the galaxy returns to normal brightness.
