A sharp radio image of blazar OJ 287’s bent jet confirms it harbors two supermassive black holes in a tight orbit.
Astronomers confirm an extreme binary black hole system at the heart of the distant blazar OJ 287
Photo Credit: Dr Efthalia Traianou, Heidelberg University, IWR
Astronomers using a global radio telescope array have captured a record-sharp image of the blazar OJ 287, showing its particle jet is sharply bent. This twisted jet provides compelling evidence that OJ 287's core contains not one but two supermassive black holes in a tight orbit. For decades, OJ 287's ~12-year cycle of flares hinted at a secondary black hole, and the new image confirms that model. In fact, this appears to be the most extreme binary black hole system ever observed. Researchers say the finding makes OJ 287 “an ideal candidate for further research into merging black holes and the associated gravitational waves”.
According to the study, using an Earth-space radio interferometer, astronomers produced an ultra-sharp image of OJ 287's center. The image shows the jet bends sharply three times within ~0.3 light-year and swings by about 30° over a few years. Such dramatic twists so close in are naturally explained by a second black hole tugging on the jet's base. This fits the picture of OJ 287's 12-year flare cycle: a ~150-million-solar-mass companion plunges through the primary's accretion disk roughly every 12 years, triggering bright outbursts and bending the jet. The observations even caught a shock wave forming in the jet, unleashing a burst of gamma rays seen by NASA's Fermi and Swift satellites. Astronomers say this twisted, ribbon-like jet is the clearest evidence yet of two supermassive black holes locked in a gravitational tug-of-war.
OJ 287's black holes will eventually merge, but that won't happen for a very long time. In the meantime, their orbit sends out ultra-long-wavelength gravitational waves that current detectors cannot pick up. Scientists expect pulsar-timing arrays – which monitor the ticking of distant neutron stars – may detect this faint gravitational-wave signal. Looking farther ahead, future space missions like ESA/NASA's planned LISA observatory (2030s) could catch the final merger of such supermassive pairs.
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