After analyzing infrared images captured by the James Webb Space Telescope (JWST), an international team of researchers has discovered multiple massive black holes approximately 12.5 to 12.8 billion years ago, actively building up with surrounding matter and growing rapidly, some of them even on the path to merging, reports a new study published on August 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 find out the role that black hole mergers played in black hole growth in their early evolutionary stages.
Researchers agree 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 of the Sun. These black holes have masses that are orders of magnitudes larger than ordinary black holes, but how they came to be this 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 that these objects are black holes collecting matter around it and growing rapidly (Figure 2).
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 surely 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.
A 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 the JWST, and rather than rely solely on the overall brightness and color of objects as researchers had done up to now, the team developed a new pixel-by-pixel color selection method that examines the color of each individual pixel in the 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, where each LRD was extremely close to the other, in the universe between 12.5 to 12.8 billion years ago (Figure 1). The distance between the two celestial bodies ranged from a few thousand to a few tens of thousand light-years, which is a distance much smaller than the 100,000 light-year length of our Milky Way galaxy.
To make sure the two LRDs were in fact close to one another, and not at different distances so to only appear aligned by 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. What they found was that it was unlikely all four pairs only appeared close, suggesting that LRDs could cluster strongly on a scale of several thousand light years (Figure 3).
Mergers are thought to be one of the mechanisms that transport large amounts of gas towards the center of galaxies, stimulating matter towards the black hole at the center. The results in 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 even further, and improve their new method by using it on a bigger sample.
Publications of the Astronomical Society of Japan
Hidden in Pixels. I. Discovery of dual “little red dots” indicates excess clustering on kilo-parsec scales
31-Aug-2026