Two black holes in orbit around each other, as observed by the RadioAstron telescope system, on the right, and an explanation of the schematic on the left.
India Joins Discovery of Binary Black Holes
Nainital: Astronomers have, for the first time, caught sight of two black holes circling each other — locked in what scientists are calling a cosmic dance.
Ordinarily, black holes remain invisible, devouring everything around them, even light. Yet, when matter spirals into their intense gravitational pull, the surroundings flare brightly enough to be seen from across the universe. Until recently, astronomers had directly imaged only two such giants — the supermassive black hole in the galaxy Messier 87 and the one at the heart of our Milky Way, Sagittarius A*. Both showed a dark silhouette encircled by a brilliant ring of light.
Now, using an extraordinary global network of telescopes — including one orbiting halfway to the Moon — a team led by Mauri Valtonen and his collaborators, including Alok C. Gupta and Shubham Kishore of the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, and A. Gopakumar of the Tata Institute of Fundamental Research (TIFR), Mumbai, has found something even more remarkable. They spotted a radio image of a distant quasar known as OJ287, powered not by one, but two black holes orbiting each other once every twelve years.
The suspicion that OJ287 might host a binary black hole system dates back to the 19th century, when astronomers first noticed its rhythmic flickering on old photographic plates. This periodic behaviour was studied in detail by Rene Hudec of the Czech Technical University in Prague. The pattern, first recognised in 1982, sparked decades of global observation, with thousands of astronomers piecing together the orbital motion of this mysterious system.
The definitive model of OJ287’s orbit emerged through two landmark papers — one published in 2018 in the Astrophysical Journal of the American Astronomical Society, and another in 2021 in the Monthly Notices of the Royal Astronomical Society (UK). The leading author, Lankeswar Dey of TIFR, worked under the guidance of Professor Achamveedu Gopakumar and Mauri Valtonen of the University of Turku, Finland.
Yet, one crucial question remained unanswered: could astronomers actually see both black holes? The binary model predicted precisely where the pair should be, but their visibility depended on whether both were luminous enough and if an image could be obtained at sufficiently high resolution.
That answer came from Shubham Kishore and Alok C. Gupta of ARIES, along with Paul Wiita of the College of New Jersey, USA. In late 2021, they monitored OJ287 using NASA’s Transiting Exoplanet Survey Satellite (TESS) and recorded a dramatic brightening — the quasar’s light intensified within just 12 hours, glowing as brilliantly as a hundred galaxies before fading away just as swiftly. Ground-based telescopes across the world, coordinated by Staszek Zola of Jagiellonian University, Krakow, confirmed the phenomenon. The observations provided strong evidence that the team had witnessed the second black hole in action.
Meanwhile, a radio image of OJ287 was captured with unprecedented clarity — sharper even than the iconic images of Sagittarius A* and Messier 87. The image revealed two bright radio sources exactly where the model had predicted them to be. This confirmation, reported by Valtonen, Gupta, Kishore, and Gopakumar in a new Astrophysical Journal paper, marks a historic breakthrough.
The achievement was made possible by the RadioAstron space telescope — a powerful antenna orbiting Earth at vast distances — working in tandem with ground-based observatories. This combination achieved a resolution far beyond any single telescope on Earth.
The resulting image showed not one, but two distinct points of radio emission. The smaller of the two black holes was seen launching a jet of high-energy particles. Because it orbits its massive partner, this jet twists and bends, resembling a wagging tail or a spinning garden hose — its changing direction betraying the smaller black hole’s orbital path.
For India, the discovery holds special significance. Scientists from ARIES, an autonomous institute under the Department of Science and Technology (DST), played a pivotal role in confirming and interpreting the findings published in the Astrophysical Journal.
Astronomers now plan to continue observing OJ287 year after year, following the evolution of its “wagging tail”. Although future observations will rely only on Earth-based telescopes with lower resolution than RadioAstron’s record-setting vision, the twisting jet will continue to reveal how the two cosmic giants dance around each other.
This discovery is not merely a visual triumph; it offers a glimpse into the universe’s far future. When these two black holes finally collide, they will unleash colossal ripples in spacetime — gravitational waves like those detected by LIGO and Virgo. In OJ287, scientists have found a natural laboratory to study the physics of such cataclysmic mergers — the very forces that shape the fate of galaxies and, ultimately, the universe itself.
– global bihari bureau
