Researchers capture first image of two black holes orbiting each other, say they may exist in pairs

Astronomers have captured an image of two black holes orbiting each other, suggesting the possibility that black holes can exist in pairs, they said.

A black hole is a region in space with such intense gravity that even light cannot escape.

The international team, including researchers from University of Turku in Finland and Aryabhatta Research Institute of Observational Sciences (ARIES) in Nainital, have imaged the black holes orbiting each other every 12 years at the centre of a quasar called ‘OJ287’ and published it in The Astrophysical Journal.

A quasar is an extremely bright galaxy core — whose light is produced when a supermassive black hole, having mass hundreds of thousands to billions of times that of the Sun at the centre of the galaxy — devours gas and dust surrounding it.

“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,” first author Mauri Valtonen, from University of Turku, said.

The pattern in light was previously thought to exist due to a rhythmic flickering of the quasar, brightening and dimming regularly over a 12-year-period, old photographs of which are said to be traceable to the 19th century. However, black holes had not been thought to exist at that time.

‘OJ287’ was “accidentally” included in pictures while astronomers focused on other objects, the researchers said.

The quasar has been monitored since then to understand if the regular change in brightness from it was due to two black holes orbiting each other at the centre and to get a complete picture of their orbiting motion.

Findings from two studies published in 2018 in ‘Astrophysical Journal of the American Astronomical Society’ and in 2021 in ‘Monthly Notices of the Royal Astronomical Society’ journals, led by Lankeswar Dey of Tata Institute of Fundamental Research in Mumbai, put forth a theory regarding orbiting black holes at the quasar’s centre.

The only question that remained was whether both black holes could be detected at the same time, the recent study’s researchers said.

Using observations from NASA’s TESS satellite, which detected light from both black holes, the researchers saw the image as a single dot and needed an image 100,000 times higher in resolution.

In this study, the astronomers compared earlier calculations with a radio image, obtained from a radio telescope ‘RadioAstron’, which captures images in the radio wavelength of light.

The two black holes were seen in the image just where they were expected to be, the researchers said, adding that the image provided an answer to the question of whether pairs of black holes exist in the first place.

“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 said.

Technology