quasar

One of the most distant extragalactic objects known, discovered in 1963. Quasars appear starlike, but each emits more energy than 100 giant galaxies. They are thought to be at the centre of galaxies, their brilliance emanating from the stars and gas falling towards an immense black hole at their nucleus. The Hubble Space Telescope has revealed that quasars exist in a remarkable variety of galaxies.

Quasar light shows a large red shift, indicating that the quasars are very distant. The furthest are over 10 billion light years away. A few quasars emit radio waves (see radio astronomy), which is how they were first identified. They are more numerous at greater distances, when we see them as they were in the early universe (since their light has taken longer to reach us). This is strong evidence that the universe has changed in the last 15 billion years, rather than being in a steady state.