by Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
After analyzing infrared images captured by the James Webb Space Telescope (JWST), an international team of researchers has discovered multiple massive black holes from approximately 12.5–12.8 billion years ago that were actively accumulating surrounding matter and growing rapidly. Some were even on the path to merging, according to a study published Aug. 31 in the Publications of the Astronomical Society of Japan.
By continuing the search for these black hole mergers using the image analysis method developed in this study and statistically measuring the proportion of massive black holes that form close pairs, researchers could determine the role black hole mergers played in black hole growth during their early evolutionary stages.
Researchers agree that there is a supermassive black hole at the center of every galaxy in today’s universe, with a mass ranging from millions to billions of times that of the sun. These black holes have masses that are orders of magnitude larger than ordinary black holes, but how they came to be so large is still unknown.
JWST, which has been operational since 2022, has identified several new types of objects in the far universe that are very small and have a characteristic red color. Named Little Red Dots (LRD), researchers think these objects are black holes collecting matter around them and growing rapidly.
A black hole merging with another black hole could explain why the black holes are growing rapidly, but until now, no one had been able to definitively identify two LRDs approaching one another. However, conventional methods may have been the problem. In the case of two LRDs very close together, current methods could have mistakenly treated them as a complex, single object.
The team of researchers led by The University of Tokyo Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) graduate student Takumi Tanaka and including Professor John Silverman analyzed high-resolution infrared images taken by JWST. Rather than rely solely on the overall brightness and color of objects, as researchers had done until now, the team developed a new pixel-by-pixel color selection method that examines the color of each individual pixel in an image.
By fine-tuning conventional methods, they searched for LRDs appearing as a single object that could in fact be two black holes on the path to merging with one another.
As a result, the researchers uncovered four sets of dual LRDs, with each LRD extremely close to the other, in the universe 12.5–12.8 billion years ago. The distance between the two celestial bodies ranged from a few thousand to a few tens of thousands of light-years, much smaller than the 100,000-light-year length of our Milky Way galaxy.
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A false-color, infrared image of an LRD taken by the JWST created using images filtered at wavelengths 1.5 µm, 2.8 µm, and 4.4 µm. The white line in the lower right corner shows the length for about 5,000 light years. Credit: COSMOS-Web / Tanaka
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Histogram of the angular separation between LRDs on the celestial sphere. Assuming a random distribution, the probability of finding two LRDs with the angular separation observed in this study would be extremely low. Credit: Publications of the Astronomical Society of Japan (2026). DOI: 10.1093/pasj/psag092
To make sure the two LRDs were in fact close to one another, rather than at different distances and only appearing aligned to observers on Earth, the researchers calculated the probability of such close pairs appearing by chance based on the number and distribution of LRDs in the area. They found it was unlikely that all four pairs only appeared close, suggesting that LRDs could cluster strongly on a scale of several thousand light-years.
Mergers are thought to be one mechanism that transports large amounts of gas toward the centers of galaxies, driving matter toward the black hole at the center. The results of this study could indicate that galaxy mergers are linked to rapidly growing black holes in the early universe. If each LRD contains a growing black hole, the black holes themselves might eventually merge as well. If true, these mergers could be detected by future gravitational-wave observatories.
The next step for the researchers will be to analyze the dual LRDs further and improve their new method by using it on a larger sample.
More information
Takumi S Tanaka et al, Hidden in Pixels. I. Discovery of dual “little red dots” indicates excess clustering on kilo-parsec scales, Publications of the Astronomical Society of Japan (2026). DOI: 10.1093/pasj/psag092
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Four ‘Little Red Dot’ pairs hint at black hole mergers in early universe (2026, August 31)
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