A huge 18-billion-solar-mass supermassive black hole lurks in the heart of an active galaxy – a quasar – 5 billion light years from Earth with a second, 150-million-solar-mass black hole companion in a steeply inclined precessing orbit. The “smaller” black hole smashes into the larger hole’s accretion disk twice every 12 years, creating flashes that can be brighter than a trillion stars.
The quasar, OJ287, has been studied for decades, allowing astronomers to infer the smaller black hole’s presence from the timing of the flashes and a slight wobble in the larger hole’s polar jet caused by gravitational interactions. The secondary black hole eluded direct detection.
“The two black holes are so close to each other in the sky that one cannot see them separately, they merge to a single point in our telescopes,” says Mauri Valtonen, an astronomer at the University of Turku in Finland and lead author of a paper in Monthly Notices of the Royal Astronomical Society.
“Only if we see clearly separate signals from each black hole can we say that we have actually ‘seen’ them both.”
Now Valtonen, his collaborator Achamveedu Gopakumar of the Tata Institute of Fundamental Research in Mumbai, India, along with an international team using telescopes around the world, have done just that, observing separate emissions from the accretion disks of both supermassive black holes.
Close analysis of a recent flare shows it was generated by the smaller black hole sucking in a massive amount of gas during its plunge through the larger hole’s accretion disk.
“According to the estimates, the flare occurred shortly after the smaller black hole had received a massive dose of new gas to swallow during its plunge,” Valtonen said. “It is the swallowing process that leads to the sudden brightening of OJ287. It is thought that this process has empowered the jet which shoots out from the smaller black hole of OJ 287. An event like this was predicted ten years ago, but has not been confirmed until now.”
Putting a bit of icing on the cake, gamma ray emissions were detected by NASA’s Fermi space telescope that were generated by the smaller black hole’s jet interacting with the gas in the larger hole’s accretion disk. As a result, OJ287 is the best candidate yet for a supermassive black hole binary and is now being routinely monitored by observatories around the world.
A NASA animation produced in 2020 shows how the smaller black hole repeatedly impacts the larger hole’s accretion disk.