JWST captures rare glimpse of early black hole growing inside network of young galaxies
Astronomers using the James Webb Space Telescope have captured one of the clearest views yet of how an early supermassive black hole may grow within a network of young galaxies. The compact active galaxy, ...
Astronomers using the James Webb Space Telescope have captured one of the clearest views yet of how an early supermassive black hole may grow within a network of young galaxies. The compact active galaxy, seen just a billion years after the Big Bang, lies beside a 12,000-parsec-long filament containing multiple galaxies that are expected to merge within a few hundred million years.
The findings, posted to the arXiv preprint server on July 6, suggest astronomers may be witnessing a short-lived phase in the evolution of rapidly growing black holes while also shedding light on how the first massive galaxies assembled in the early universe.
Too big for its galaxy
Since JWST began operating, astronomers have found a population of compact, actively feeding black holes in galaxies from the universe's first billion years. Many of these black holes appear far too massive for their host galaxies, with some appearing 10 to 100 times heavier than expected.
This particular black hole, in a galaxy known as GN-77652, is observed at a redshift of 5.23. It weighs about 11 million solar masses, while its host galaxy contains only around 170 million solar masses worth of stars, placing it at roughly 300 times the mass expected from a relation seen between black holes and their galaxies in the nearby universe.
Crowded home
Led by Giulia Tozzi of the Max Planck Institute for Extraterrestrial Physics, the team used JWST's NIRSpec integral field spectrograph, as part of the BlackTHUNDER program, alongside deep NIRCam imaging to map the region around GN-77652 in detail.
What they found was a bustling environment containing four additional galaxy-sized clumps of gas and stars, labeled B, C, D and E, all sitting at essentially the same redshift. These clumps were spread across the filament at distances of roughly 2.4 to 11.6 kiloparsecs from GN-77652.
Interestingly, GN-77652 is not the most massive galaxy in the group. Sources B and D are each 10 times heavier in stars. Gas across the whole structure appears to converge toward source B, near the center of the complex, hinting that the entire system may eventually merge into one.
The five sources differ by up to an order of magnitude in stellar mass, star formation rate and chemical enrichment, suggesting each component is at a different stage of evolution.
GN-77652 itself shows a shallow, resolved velocity gradient consistent with a small rotating gas disk. The team explains in the paper that this unique feature, confirmed in only a handful of these compact black hole hosts so far, is "consistent with dominant gravity driving"—the same pattern seen in normal star-forming galaxies at these redshifts—suggesting GN-77652 behaves more like a settled galaxy than a violently disturbed one.
Signs of a twin?
The most striking result comes from source B, sitting just 2.4 kiloparsecs (in projection) from GN-77652. The diagnostic emission-line ratios there point to gas being ionized by something more energetic than starlight alone.
To test whether this ionization could simply be light from GN-77652 reaching over and lighting up B's gas, the team calculated how much ionizing radiation would be required.
They found the incident luminosity needed was more than two orders of magnitude higher than what GN-77652's black hole could plausibly supply—ruling out GN-77652 as the source and pointing to a second, distinct black hole in B. If confirmed, this would be one of the very few known dual black hole pairs at such a close separation this early in the universe's history.
The team also tested whether GN-77652's black hole could have formed through "direct collapse"—a process in which a dense cloud of gas collapses directly into a massive black hole seed, skipping the intermediate step of forming stars first. Measuring the radiation field produced by the surrounding filament, they found it falls just short of the intensity such a process would require.
The researchers note that stronger radiation may have been present at earlier times or that other explanations remain viable—including the possibility that GN-77652's black hole is a primordial black hole, or one flung out of a neighboring galaxy through gravitational interactions.
A temporary phase
Based on the separations and masses involved, the team calculates the whole cluster of galaxies should merge into one within roughly 150 to 440 million years. Modeling how the merged system's black hole and stellar mass might grow over that time, they find the ratio between the two would settle much closer to what's seen in typical galaxies today.
The team concludes that GN-77652's compact, overmassive appearance likely represents a short-lived evolutionary phase, consistent with the broader trend of such objects becoming rarer at lower redshifts as the universe ages.
The team says follow-up JWST spectroscopy targeting more emission lines at higher resolution will be needed to confirm the second black hole in source B and to better track how this system evolves over cosmic time.
Written for you by our author Shreejaya Karantha, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.
Publication details
Giulia Tozzi et al, BlackTHUNDER Reveals a Massive Filament around a Compact AGN at z ≃ 5.23, arXiv (2026). DOI: 10.48550/arxiv.2607.05523
Who's behind this story?
Shreejaya Karantha is a science writer and astronomy communicator based in India, with a focus on astrophysics and the early universe. Full profile →
BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries. Full profile →
Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →
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