A vast number of Galaxies in the Universe have a central black hole that is incredibly massive. The Black Hole at the centre of the Milky Way, dubbed Sag A*, is estimated to have a mass as high as three Million Suns. We generally can’t see black holes, but when they start to pull in matter from surrounding gas and dust clouds, the material forms a disk around the star. This accretion disk can heat up to incredible temperatures and emit X-rays and other high energy light, allowing us to see where the black holes are. Sometimes the light from the accretion disk can outshine the entire host Galaxy of the black hole. When this happens we call the object a quasar.
What if two Galaxies with Supermassive black holes were to merge? Would the black holes eventually merge with each other? This is what the best theories predict, but we have never observed it in real time, nor have we been able to simulate the merger. Problems with simulations are dubbed the ‘final parsec problem,’ where the theories cannot predict what the final stages of a black hole merger will look like. It makes sense too, since we’re dealing with the most elusive and enigmatic physical objects in the Universe. There may be some elusive physics concepts we haven’t even discovered yet that are happening during the final merger.
Observations may give us a view of a merger in action for the first time ever. Observations of a distant quasar reveal a repeating light signal, which may be the result of two supermassive black holes in the final stages of a merger.
“The end stages of the merger of these supermassive black hole systems are very poorly understood,” says the study’s first author, Matthew Graham, a senior computational scientist at Caltech. “The discovery of a system that seems to be at this late stage of its evolution means we now have an observational handle on what is going on.”
The discovery could only be made with continual observation of quasar sources, and is a direct reflection of the new technology that has characterized modern astronomy. The data came from the Catalina Real-Time Transient Survey (CRTS), using three ground telescopes in the United States and Australia to continuously monitor 500 million light sources strewn across the majority of the night sky.
“Until now, the only known examples of supermassive black holes on their way to a merger have been separated by tens or hundreds of thousands of light years,” says study coauthor Daniel Stern, a scientist at NASA’s Jet Propulsion Laboratory. “At such vast distances, it would take many millions, or even billions, of years for a collision and merger to occur. In contrast, the black holes in PG 1302-102 are, at most, a few hundredths of a light year apart and could merge in about a million years or less.”
So we won’t actually get to watch the merger happen, unless we are still watching it in a Million years or so, but the fact that the Black Holes are far closer together than any merging pair ever observed before is astounding. By studying the merger and the light from the black holes, we can learn about how black holes merge past the final parsec, and gain insights into how they behave in general.