Published in the Astronomical Society of Australia, Chris Onken, an astrophysicist at the ANU, explains how they were able to determine the rate at which a black hole grows: by measuring its brightness (or its luminosity). “As more and more objects fall into the black hole, this material – like a bullet rolling down the hill – increases in speed and there is a lot of friction in the gas falling into the black hole. The gas then becomes very hot and glows up to, in this case, more than half of the universe. This black hole eats the equivalent of 80 of our suns every year, or one Earth every second“, he explains in Cosmos Magazine. This light still took 7 billion years to reach the Earth.
This black hole, which is therefore around 7 billion years old, is the one that is growing the fastest in comparison with all the other black holes studied by the team, up to 9 billion years ago. The team doesn’t yet know for sure what makes it so bright though, so far they’re looking at two large galaxies colliding, suddenly giving the black hole enough “food” to grow so rapidly. “If you look at these systems much earlier in the history of the universe, that’s when there was a lot more mergers between galaxies“, continues Chris Onken.