Quasars give off nearly 1,000 times the amount of energy that the Milky Way emits. These quasars emit so much energy that astronomers speculate that the most probable power source for a quasar is a supermassive black hole, according to Sloan Digital Sky Survey.
The supermassive black hole that sits at the center of a quasar is surrounded by a rotating ring of gas. This mass of gas then falls into the black hole and is heated to millions of degrees. The heated gas then emits very powerful thermal radiation that spans the visual spectrum. According to Sloan Digital Sky Survey, quasars are the brightest objects in the universe. The closest quasar to Earth is around 800 million light-years away. Because of this, it is possible to assume that the last quasar died out 800 million years ago.