Quasars are exceptionally luminous star-like sources of radiation with very high red shifts.
They have intensities between 1012 and 1015 times that of the Sun which means that a single quasar may emit about 1000 times as much energy as our galaxy!
The radiation from quasars is now thought to originate a vast disc of gas, known as an accretion disc, that has been attracted towards the event horizon of a super-massive at the centre of a galaxy. The enormous gravitational pull of the black hole causes the gas to rotate at high speed creating huge frictional forces within it.
The enormous speeds of molecules within this gas cloud generate a fantastically high temperature which results in the emission of light of unbelievable intensity.