Of all the discoveries from the James Webb Space Telescope, the multitude of Little Red Dots it has observed is among the most enigmatic. Now, simulations using the Japanese Supercomputer ATERUI III have explained the nature of the Little Red Dots without requiring any exotic assumptions. The simulations show that the Little Red Dots are black holes growing at a rate that would be impossible today because of conditions in the early universe.
In the study, published in the journal Nature, a research team led by Sunmyon Chon at the Max Planck Institute for Astrophysics used the ATERUI III supercomputer at the National Astronomical Observatory of Japan to conduct the most detailed cosmological simulations to date of conditions in the early universe.
The team’s simulation started with the conditions surrounding a galaxy in the early universe, then zoomed in to individual gas clouds. These computationally intensive simulations were made possible by ATERUI III’s high-resolution computing power.
The simulations show that in the early universe, intense far-ultraviolet (FUV) radiation from nearby galaxies suppresses star formation in gas clouds, so rather than forming many small stars, the gas can form a single supermassive star, which then collapses into a black hole seed. The simulations show that, once formed, these black hole seeds are surrounded by dense gas disks.
This environment traps radiation, enabling the black holes to grow at rates dozens of times faster than would be possible in the modern universe. The simulated properties of these rapidly growing black holes provide a good match to the Little Red Dots (LRDs) observed by the James Webb Space Telescope (JWST).
A race against cosmic time
A long-standing mystery in astronomy has been how the supermassive black holes, with masses millions or even billions of times that of the sun, observed in the early universe appeared so quickly, less than 600 million years after the Big Bang.
JWST was expected to answer this question by allowing us to see fainter, more distant galaxies. Because light travels at a finite speed, looking at more distant objects is like looking back in time. When we observe a galaxy 11 billion light-years away, that light has had to travel 11 billion years to reach us.
That light shows us what the galaxy looked like when the light left 11 billion years ago. Likewise, the light from a galaxy 12 billion light-years away is 12 billion years old.
JWST allows us to look back farther in time than ever before, but instead of finding the answer to the rapid growth of black holes, it revealed a population of small, enigmatic, extremely red objects dubbed Little Red Dots (LRDs).
Little Red Dots explained
These new simulations show that the LRDs are the answer to the black hole growth mystery—and a deceptively simple answer at that. In the simulation, these results happened as a natural consequence of conditions in the early universe, without requiring any exotic assumptions or chance accidents. This is important for explaining the ubiquity of LRDs.
As JWST continues to reveal more LRDs and future telescopes probe deeper into the early universe, this new model provides a powerful roadmap for understanding how the cosmos evolved. https://phys.org/news/2026-09-japanese-supercomputer-simulations-webb-red.html
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