Detailed image shows unusual structure of the emitted plasma jet – two supermassive black holes assumed to be merging in the galaxy core

For more than 150 years, the OJ 287 galaxy and its brightness variations five billion light years away has both puzzled and fascinated astronomers, because they suspect two supermassive black holes are merging in the core. An international research team led by Dr Efthalia Traianou of Heidelberg University recently succeeded in taking an image of the heart of the galaxy at a special level of detail. The groundbreaking image, taken with the aid of a space radio telescope, shows a heretofore unknown, heavily curved segment of the plasma jet spinning off the galaxy’s center. The image provides new insights into the extreme conditions that prevail around supermassive black holes.

The core of the OJ 287 galaxy belongs to the class of blazars that exhibit high activity and striking luminosity. The driving forces behind these active galactic cores are black holes. They absorb matter from their surroundings and can fling it off in the form of giant plasma jets comprised of cosmic radiation, heat, heavy atoms, and magnetic fields. “We have never before observed a structure in the OJ 287 galaxy at the level of detail seen in the new image,” emphasizes Dr Traianou, a postdoctoral researcher in the team of Dr Roman Gold at the Interdisciplinary Center for Scientific Computing of Heidelberg University.

The image, which penetrates deep into the galaxy’s center, reveals the sharply curved, ribbon-like structure of the jet; it also points to new insights into the composition and the behavior of the plasma jet. Some regions exceed temperatures of ten trillion degrees Kelvin – evidence of extreme energy and movement being released in close proximity to a black hole. The researchers also observed the formation, spread, and collision of a new shock wave along the jet and attribute it to an energy in the trillion-electron volt range from an unusual gamma ray measurement taken in 2017.

The image in the radio range was taken with a ground-space radio interferometer consisting of a radio telescope in Earth’s orbit – a ten-meter-long antenna of the RadioAstron mission on board the Spektr-R satellite – and a network of 27 ground observatories distributed across the Earth. In this way, the researchers were able to create a virtual space telescope with a diameter five times greater than the diameter of the Earth; its high resolution stems from the distance of the individual radio observatories to one another. The image is based on a method of measurement that takes advantage of the wave nature of light and the associated overlapping waves.

The interferometric image underpins the assumption that a binary supermassive black hole is located inside galaxy OJ 287. It also provides important information on how the movements of such black holes influence the form and orientation of the plasma jets emitted. “Its special properties make the galaxy an ideal candidate for further research into merging black holes and the associated gravitational waves,” states Efthalia Traianou.

Institutions from Germany, Italy, Russia, Spain, South Korea, and the US all contributed to the research. It was supported by various research and funding institutions. The research results were published in the journal “Astronomy & Astrophysics”.