The sluggish dance of supermassive black holes

- EN - DE

Large-scale observing campaign provides new insights into black-hole pair at the center of active galaxy OJ 287.

The left partial image shows OJ 287 in the center on an image taken by the space
The left partial image shows OJ 287 in the center on an image taken by the space-based Swift telescope in ultraviolet light. The source of the ultraviolet light is the core region of the active galaxy OJ 287, but its substructure cannot be resolved further with this telescope. The right subimage shows an artist’s rendering of this core, including the matter disk, the jet, and the postulated pair of second black holes. Here, the lower-mass and smaller black hole orbits the primary black hole. S. Komossa et al.; NASA/JPL-Caltech

A long-term study using data from four telescopes ranging from the radio to the high energy frequency range penetrates to the core of the much-discussed active galaxy OJ 287, revealing more details about what is happening inside it. The results of the international team led by Stefanie Komossa of the Max Planck Institute for Radio Astronomy consolidate the evidence for a system of two black holes and once again put the primary black hole on the scale.

Blazars are a special class of galaxies characterized by high activity and extreme luminosity. The driving engines of these galaxies are black holes hidden in their cores, millions to billions of times heavier than our Sun. In the past of the universe, these engines ran at full speed whenever they received fresh fuel in the form of matter from the collision of two galaxies. The subsequent merger of the two galaxies creates supermassive binary black holes. The study of such black-hole pairs reveals much about the evolution of galaxies and the growth of black holes.

Black hole on the scale

OJ 287 is one of the few active galaxies where there is strong evidence for such a massive double black hole system. One indication are radiation bursts, which are directly due to the processes in the center of the galaxy. These repeat every 11 to 12 years and, strictly speaking, consist of two increases in brightness each about a year apart. While this behavior is almost certainly due to two orbiting black holes, there are a number of possible scenarios for what such a system might look like. The team led by Stefanie Komossa of the Max Planck Institute for Radio Astronomy has now revised the previously favored model by means of an unprecedented observational campaign. For the first time, the researchers have also directly determined the mass of the primary black hole. At 100 million solar masses, this is likely to be about a hundred times lighter than previously assumed, and at the same time explains the entire history of OJ 287’s radiation outbursts, which has now been measured in detail.

Glimpses into the Invisible

The galaxy OJ 287 is too far away to spatially resolve the compact core region around the suspected black holes with telescopes. However, since this region dominates the brightness of the entire galaxy, the radiation emanating from it can not only be easily detected from Earth - its study also allows the processes hidden in the bright core to be reconstructed with certain constraints. It is helpful to know the source of energy and the underlying processes. Matter channeled in a disk toward the dominant supermassive black hole emits gravitational energy in the form of radiation in the optical and ultraviolet spectral regions. A jet originating in the center of this matter disk around the primary black hole accelerates particles out of the galaxy core in a narrow jet. This produces strong radiation from the radiobis to the x-ray and gamma-ray regions.

OJ 287 is an excellent laboratory to study the physical conditions prevailing in one of the most extreme astrophysical environments: disks and jets of matter in close proximity to one or two supermassive black holes," says Stefanie Komossa of the Max Planck Institute for Radio Astronomy, first author of the two studies now published. That’s why we initiated the Momo project (Multiwavelength Observations and Modeling of OJ 287). It makes use of densely timed observations of OJ 287 at more than 14 frequencies from the radio to the high-energy range, spanning years, as well as special follow-up observations from multiple ground- and space-based observatories when the blazar is found in unusual states."

The recurring brightness peaks of OJ 287 can be explained in the double black hole system model in particular by the motion of the second, lower-mass black hole orbiting the primary black hole. On its inclined orbit, it disturbs either the jet or the matter disk of the more massive black hole, causing OJ 287’s periodically recurring bursts of brightness. Measurements with the 100-meter Effelsberg radio telescope attribute the most recent burst directly to the jet. It is like looking into a glaring spotlight that outshines everything behind it.

Strong evidence for two supermassive black holes in the core.

The previously common model for the processes in the center of OJ 287 assumed a primary black hole ten billion times heavier than the Sun. According to this model, the next radiation surge would have been expected in October 2022 - a prediction that was not confirmed. Instead, thanks to the close-meshed data from the Momo campaign, astronomers discovered this burst much earlier, between the years 2016 and 2017. As a result, the previous model lost its validity. The researchers now assume a hundred times lighter black hole, whose mass could be independently confirmed. It also follows that the orbit of the presumed secondary black hole around the primary should tumble less than previously thought. This behavior has direct implications for the expected brightness bursts, which are in agreement with the new measurements. ,,This result is very important because the mass is also a key parameter in the models that study the evolution of such a binary system. How far apart are the black holes, how fast will they merge, how strong is their gravitational wave signal," says Dirk Grupe of Northern Kentucky University (USA), a co-author of both studies.

Gravitational waves and a photo?

The MOMO results make the authors optimistic to be able to detect gravitational waves of this or similar binary systems with future space-bound observatories. It may even be possible to spatially resolve the two black holes in OJ 287 with a large network of radio telescopes, such as the Event Horizon Telescope familiar from the media or the Square Kilometre Array still under construction. This would be the first direct detection of a close system of two supermassive black holes in the center of a galaxy.

Multifrequency radio variability of the blazar OJ 287 from 2015-2022, absence of predicted 2021 precursor-flare activity, and a new binary interpretation of the 2016/2017 outburst