Astronomers have confirmed the presence of a second supermassive black hole in the turbulent heart of a distant galaxy.
The scientists also found that both of these cosmic monsters are feeding on gas and dust and that one has a peculiar oblong orbit that sends it plunging through a massive disk of red-hot dust and gas around its companion.
The second black hole behemoth found at the center of OJ 287, a galaxy located around 5 billion light-years away, has a mass of about 150 million suns. As intimidating as that is, the black hole it orbits is even more massive — equivalent to over 18 billion suns — and is greedily feeding on surrounding gas and dust in the form of an accretion disk.
Matter from this violent cosmic whirlpool that doesn't fall to the surface of this supermassive black hole is channeled to its poles and is blasted out as powerful jets in a process that makes the galactic center shine brightly as a type of active galactic nucleus (AGN) called a quasar.
It was in this accretion disk that astronomers spotted signals of a second orbiting supermassive black hole. As that second black hole plunges through the accretion disk surrounding the main black hole, it triggers a series of flares.
These flares arise as the diving black hole heats the disk of material and causes it to "burp" out hot gas as expanding bubbles. The gas bubbles cool over a period of months, radiating light and emitting flashes that last around two weeks and are brighter than the combined light from a trillion stars or the entire light output from the Milky Way.
The new research accurately predicts the timing of the second black hole's dives through the accretion disk, thus allowing astronomers to model both the flattened, oblong orbit of the second black hole and the timing of the accretion-disk flares it creates.
Despite matching prior predictions, the new observations still delivered some surprises. For example, the astronomers spotted types of flares that hadn't been detected before, including a massive flare that was 100 times brighter than an entire galaxy and lasted just a day.
"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."
When the secondary black hole dove through the accretion disk of its larger partner, it also created a powerful burst of gamma-rays — the largest seen from this system in six years — that was observed by the Fermi Gamma-ray Space Telescope. The gamma-ray blast was created by a jet of material from the secondary black hole hitting the gas in the main accretion disk. This was confirmed when the scientists looked back through archival data and saw a similar gamma-ray burst in 2013 — the last time the smaller black hole dropped through the accretion disk.
"So what about the one-day burst? Why have we not seen it before?" Valtonen said. "It turns out that we have simply just had bad luck. Nobody observed OJ287 exactly on those nights when it did its one-night stunt."