What enables quasars to be so bright?
A quasar is a disc of matter just outside the event horizon of a super massive black hole. The actual event horizon (point where the gravity of the black hole is inescapable) is also called the Schwarzschild radius (technically the point where escape velocity would be the speed of light). A Quasar will start at the Schwarzchild limit and go out anywhere from 10 radii to 10,00 radii. Considering the Schwarzchild limit of the super massive black hole at the center of the Milky Way is estimated to be about 10 times the diameter of the sun. So we are looking at an object that is 100 times the diameter of the sun to 100,000 times the diameter of the sun.
So imagine a disc from a point about 1/4 the way to Mercury out to the orbit of the Earth. Now imagine that disc is one big ring of matter. That would be a lot of matter and therefore would be generating a lot of energy. Now the smallest Quasar would be about that size. The largest Quasar would be about the diameter of the whole solar system. Since the vast majority of the solar system is empty space, and a quasar is potentially no empty space...the amount of mass we are looking at is estimated to be as high as 10 billion times the mass of the entire solar system.