An international team aligned space and ground radio telescopes to resolve two compact emitters at the quasar's center and matched their locations to long-running orbital models. Prior images had resolved single black holes in the Milky Way and Messier 87, but never a bound pair in mutual motion.
"Quasar OJ287 is so bright that it can be detected even by amateur astronomers with private telescopes. What is special about OJ287 is that it has been thought to harbour not one but two black holes circling each other in a twelve-year orbit, which produces an easily recognisable pattern of light variations in the same period," says first author Mauri Valtonen of the University of Turku. The findings appear in The Astrophysical Journal.
Historic glass-plate photographs trace OJ287 back to the 19th century, when it was captured incidentally while astronomers targeted nearby objects. In 1982, Aimo Sillanpaa identified the quasar's 12-year cyclic brightening, inspiring decades of monitoring to test the binary hypothesis and pin down the orbit.
Recent work solved the orbital geometry, but the open question was whether both black holes could be seen at once. NASA's TESS mission detected light from both, though optical images lacked the angular resolution to separate them. Radio interferometry delivered the 100,000-times sharper view needed to distinguish the pair.
"For the first time, we managed to get an image of two black holes circling each other. In the image, the black holes are identified by the intense particle jets they emit. The black holes themselves are perfectly black, but they can be detected by these particle jets or by the glowing gas surrounding the hole," Valtonen says.
The team also reports a previously unseen, twisting jet from the smaller black hole, likened to a rotating garden hose. Because the secondary orbits rapidly, its jet direction wobbles like "a wagging tail," and should swing measurably as the object changes speed and orbital phase in coming years.
"The image of the two black holes was captured with a radio telescope system that included the RadioAstron satellite. It was in operation a decade ago, when OJ287 was imaged. The satellite's radio antenna went half-way to the Moon, which greatly improved the resolution of the image. In recent years, we have only been able to use Earth-based telescopes, where the image resolution is not as good," Valtonen says.
Research Report:Identifying the Secondary Jet in the RadioAstron Image of OJ 287
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University of Turku
Understanding Time and Space
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