For the first time, a group of astronomers has captured the cosmic dance of two supermassive black holes orbiting each other.
For the first time, a radio image showing two supermassive black holes orbiting each other has been taken, confirming a prediction about a phenomenon previously only observed indirectly.
The astronomical picture takes shape in the quasar OJ287, about 5 billion light years away from Earth in the constellation Cancer. Quasars are extremely active galactic nuclei, powered by supermassive black holes that devour gas and dust, heating the material to the point of emitting very intense radiation.
High resolution. The radio image was obtained by combining observations from ground-based radio telescopes with those from the now-defunct Russian RadioAstron (Spektr-R) satellite, whose orbit extended to about halfway to the Moon. This enabled resolutions up to 100,000 times higher than those of conventional optical images.
David vs Goliath. In detail, it is observed that the largest black hole has a mass estimated at approximately 18 billion times that of the Sun, while its much smaller companion weighs approximately 150 million solar masses.
The system follows a 12-year orbit; this period was already known since the 1980s, when a regular variation in the brightness of the quasar was noticed, interpreted as the effect of the presence of two bodies in orbit, but it was not possible to differentiate one from the other. Among other things, it should be remembered that the quasar OJ287 has been under observation for over a century, so much so that there are photographic plates from the late nineteenth century that depicted it.
The dance. “One of the most visible results concerns the jet of particles – or “jet” – emitted by the smaller black hole, which appears “twisted”, like a rotating garden hose, due to its rapid orbital motion around the more massive companion”, explains Mauri Valtoren of the University of Turku (in Finland) who published the research in The Astrophysical Journal. When the researchers overlaid the radio image on previously developed theoretical models, they saw that the positions of the jets matched what was mathematically predicted: the two bodies appeared right where they were supposed to be.
Why it matters. Until now, binary black hole systems had only been confirmed indirectly through observations of gravitational waves or variations in brightness. This is the first time we get a direct visualization, distinguishing the two objects separately.
The observation offers a unique opportunity to study in real time how radio jets evolve, in particular the “tail-wagging” jet (“wagging tail“) of the secondary black hole.
This will allow the dynamic models of gravitational interaction to be verified in the coming years.
Aspects still open. Although the image is very clear, scientists point out that the jets could overlap, which would complicate interpretation: it is not excluded that some emissions come from very close or even intersecting regions. Unfortunately, the RadioAstron satellite is no longer active, so obtaining equally resolute images in the future will require other technological solutions or new missions.