Within most galaxies there lurks a supermassive black hole. Our own galaxy, for example contains a black hole 4 million times more massive than our Sun. One of the big mysteries of these black holes is just how they formed, and how long it took for them to reach such a massive size. Now a massive black hole at the edge of the observable universe challenges our understanding of them.
We discovered this distant black hole because it is a quasar. When a black hole captures nearby material, the material becomes superheated and radiates powerful radio energy and x-rays. These beacons of light are so bright they can only be powered by supermassive black holes. By observing the brightness of distant quasar we can calculate the mass of its black hole engine.
Recently astronomers discovered the most distant quasar ever. Known as J1342+0928, it is so distant we see it from a time when the universe was only 690 million years old. At that time galaxies were just starting to form. But this quasar gives off so much light that its black hole must be 800 million times the mass of our Sun. So how did this particular black hole get so massive so soon? It’s possible that it exists in a rather dense region of space. Having lots of matter around would make it easier to grow quickly. But that isn’t enough to solve the mystery, because the faster a black hole consumes matter, the more light the matter would emit, and that pressure of light and heat would tend to push matter away from the black hole. It’s known as the Eddington limit, and it puts an upper bound on how fast a black hole can grow. To reach 800 million solar masses in such a short time, the black hole would have to consume matter fairly close to this limit.
The big question about this black hole is whether it is simply an unusually early bloomer, or if it is rather typical of black holes in the early universe. To answer that question we will need to find more examples of large quasars on the edge of the cosmos. So the race is on to find these most distant of beacons. If we can find them, they will help us understand how supermassive black holes and their galaxies formed.