Astronomers have observed the distant active galaxy OJ 287 for many years. It’s a BL Lac object, a type of active galactic nuclei known for their extreme variability. They display rapid and pronounced variability in their brightness across multiple wavelengths.
In simple terms, an active galactic nuclei is a supermassive black hole (SMBH) that’s actively accreting material. SMBHs exert an extraordinarily powerful influence on their surroundings. Observing the formation and propagation of jets that come from SMBHs are one way to understand how they dominate their environments. Among other effects, these jets heat up nearby gas clouds, stifling their star formation.
New observations with a radio interferometer named Radioastron Space VLBI revealed the presence of an unusual ribbon-like jet of material emanating from the center of OJ 287. The observations and results are in a recent paper titled “Revealing a ribbon-like jet in OJ 287 with RadioAstron.” The lead author is Dr. Thalia Traianou from Heidelberg University, and the paper is published in Astronomy and Astrophysics.
The RadioAstron Space VLBI mission combines a spaceborne radio telescope with 27 ground-based radio telescopes worldwide to create a large virtual telescope. Using interferometry, it creates a virtual radio telescope that’s five times Earth’s diameter. This gives RadioAstron exceptionally high spatial resolution, allowing the telescope to peer into OJ 287’s core. Over several years of observations, it found a long, sinuous, ribbon-like jet of plasma that twists and turns as it reaches into space.
While this jet has been spotted before, and is the site of a historic detection of an extremely energetic shock, this is the first time astronomers have observed the twists and turns. “For the first time, due to a favorable geometrical position of the jet in tandem with high data quality, we detect multiple sharp bends that form a “ribbon-like” jet structure that extends down to 1 mas,” the authors write in their research article.
These are multi-epoch VLBI images of OJ 287 observed on May 3, 2014, April 11, 2015, April 22, 2016, and April 16, 2017. The ridgelines, delineating the jet’s axis for each epoch, are overlaid as dashed lime lines, with a black outline for enhanced visibility. This image sequence clearly shows the jet’s evolution over the four years. Image Credit: Traianou et al. 2025. A&A
RadioAstron detected more than just the ribbon-like jet. It also also found regions within the jet with temperatures greater than 10 trillion Kelvin. That’s extremely hot. The Sun’s core is about 15 million Kelvin, for comparison, meaning that the hot regions in the jet are 660,000 times hotter. This temperature is similar to the Universe only microseconds after the Big Bang, when all matter existed as quark-gluon plasma.
They also found the emergence of a new jet component. It’s a new shock wave in the jet that slammed into a pre-existing stationary shock. It coincides with the historic detection of a massive outburst of energy in 2017 that released trillion-electron-volt gamma rays from OJ 287.
“We captured the birth of a jet component and watched it travel down this beautiful ribbon until it hit a shock wave and produced the most energetic gamma rays ever detected from this source,” said lead author Traianou in a press release.
The new RadioAstron observations of OJ 287’s twisted jet may help explain a long-standing puzzle.
Astronomers have been observing OJ 287 for well over a century, logging the object’s brightness variations. They follow an unusual 60-year cycle, and a shorter 12-year cycle of extremely luminous flares. The cyclical variations suggest that the galaxy hosts a pair of black holes. This could not only create the cycle, but could also explain why the jet is twisted like a ribbon. If two black holes are orbiting each other, their motion could twist the jet.
“These periodic variations are explained well by a supermassive black hole binary (SMBHB) model in which a secondary supermassive black hole follows a precessing, eccentric orbit around a more massive primary,” the authors explain. “Flares are generated each time a smaller component crosses the primary’s accretion disk.”
These images of OJ 287 are from April 25, 2016. The image on the left shows brightness temperature. The image on the right shows total intensity contours. P1, P2, and P3 are polarized features, and the central dashed green curve traces the jet ridgeline. Yellow circles C1 and C2 mark the locations of the black holes. Image Credit: Traianou et al. 2025. A&A
Finding a galaxy with a pair of black holes presents a new opportunity. Eventually, the pair will likely merge and produce gravitational waves. Astronomers have detected these waves from many mergers, so OJ 287 is a chance to observe a pair of SMBH before they merge. While RadioAstron ended in 2019, observations of OJ 287 with other facilities will be ongoing.
“One of the beautiful things about fundamental science is the unpredictability of its impact. When electricity was discovered two hundred years ago, no one could have imagined how deeply it would shape modern society, said co-author Professor Leonid Curvits from the Faculty of Aerospace Engineering at Delft University of Technology in the Netherlands. “It’s the same with our research: we don’t know when and what its effects will be. But that uncertainty is part of what makes fundamental science so exciting. That said, it is certain that this RadioAstron study is a prelude to the upcoming transformational discoveries in the new era of multi-messenger astronomy.”