Quasars

A quasar is an extremely bright and distant active galactic nucleus. They consist of a compact halo of matter surrounding a super massive black hole at the centre of a young galaxy.

The term quasar comes from "quasi-stellar radio source" which means star-like emitter of radio waves. We now know that most quasars don't emit a lot of radio waves but do emit light, infra-red, ultra-violet and gamma rays, nevertheless the name has stuck. They are one of the brightest objects in the Universe, so bright we don't see the light from other stars in the galaxy they are part of. We can see quasars 12 billion light years away they are so bright.

At the centre of the quasar is a very large black hole sucking in super hot gas at an incredible rate. As the gas spirals into the black hole a huge amount of energy is generated, a trillion times more than our Sun emits. Not all the gas is sucked in, some of it escapes as a hot wind which is blown away from the disc at an incredible speed.

Quasars are amongst the earliest known objects in the Universe. the light from some of them shows a massive red shift, sometimes suggesting that they are around 12 billion light years away. When we look at quasars we are looking at the very young Universe.

pics courtesy of NASA

The Hubble image above shows the quasar 3C273, firstly as a brilliant point of light and then with the centre covered, so that the surrounding host galaxy can be observed.