One of the things the James Webb Space Telescope revealed to us is a class of small, distant galaxies in the very early Universe. Their light has been stretched into the red after billions of years travelling in the expanding Universe, and they've been dubbed Little Red Dots (LRD). Initially, the JWST couldn't reveal their true nature because LRDs are near the limits of the powerful telescope's observational power. But we know they're there; the genie's out of the bottle.
What followed is science at its best, as researchers around the world pored over the data and tried to determine what they were seeing. One explanation bubbled to the top of the scientific fermentation: LRDs are primordial galaxies with active galactic nuclei and supermassive black holes (SMBH). This is counter to what astrophysicists think they know about the Universe, since finding such massive black holes so soon after the Big Bang doesn't agree with theory. Also, critically, LRDs don't behave like other AGN and SMBH. For one thing, they don't emit x-rays, a hallmark of AGN.
Other potential explanations are found in the scientific literature, too. Research covered here at Universe Today showed that a nearby dwarf galaxy, a satellite of the Milky Way, may contain a much more massive black hole than thought. In that galaxy, the black hole was 4.5 times more massive than all the stars in the galaxy combined, which is a very rare relationship. The researchers in this case postulated that dwarf galaxies could be relic LRDs from the early Universe.
Now, astronomers working with the JWST have found an LRD that seems to host an actively growing SMBH. The discovery is in research titled "Extreme properties of a compact and massive accreting black hole host in the first 500 Myr," which is published in Nature Communications. The lead author is Roberta Tripodi from the Faculty of Mathematics and Physics at the University of Ljubljana in Slovenia and the Institute for Fundamental Physics of the Universe in Trieste, Italy.
The galaxy in question is named CANUCS-LRD-z8.6, and the JWST observed it as it was only about 570 million years after the Big Bang. Just like other LRDs, this one's black hole is far more massive than expected. The JWST's NIRSpec instrument found key features in the galaxy's spectra that strongly suggest it hosts an actively accreting black hole. "Understanding how these massive BHs formed in such compact galaxies as early as redshift z = 8.6 remains a key question," the authors write in their research article.
“The spectral features revealed by Webb provided clear signs of an accreting black hole at the centre of the galaxy, something that could not have been observed with previous technology." - Dr. Nicholas Martis, University of Ljubljana
"This discovery is truly remarkable," lead author Tripodi said in a press release. "We’ve observed a galaxy from less than 600 million years after the Big Bang, and not only is it hosting a supermassive black hole, but the black hole is growing rapidly - far faster than we would expect in such a galaxy at this early time. This challenges our understanding of black hole and galaxy formation in the early Universe and opens up new avenues of research into how these objects came to be."
"Indeed, this source is unique in terms of its BH and host galaxy properties, being the only high-z source to date that shows evidence of broad line emission and high-ionization lines," they write in their article.
When researchers examined the JWST's spectra from CANUCS-LRD-z8.6, they found clear signs of an actively accreting black hole. Broad line emissions are produced when material is orbiting very close to a BH and moving at extremely high velocities. High-ionization lines come from atoms that have had electrons stripped away by intense radiation in extreme conditions, another hallmark of black holes. The spectra also showed that the SMBH is unusually large for such an early time in the Universe. They also found that the galaxy lacks heavy elements, which indicates that it's in the early stages of evolution.
"The data we received from Webb was absolutely crucial,” added co-author Dr. Nicholas Martis from the University of Ljubljana, who helped analyse the spectrum of the source. “The spectral features revealed by Webb provided clear signs of an accreting black hole at the centre of the galaxy, something that could not have been observed with previous technology. What makes this even more compelling is that the galaxy’s black hole is overmassive compared to its stellar mass. This suggests that black holes in the early Universe may have grown much faster than the galaxies that host them."
The researchers developed a physical model of CANUCS-LRD-z8.6 that can account for its observations and its derived properties. In this hypothesized model, our line of sight to the AGN is not heavily obscured by dust. Instead, the majority of the stellar light is coming from stars still embedded in the gas clouds they formed in, which leads to high obscuration. Previous research shows that even small amounts of dust in a LRD can create significant obscuration because they're so compact.
*This simple schematic represents the model the researchers developed to explain their findings. "Components include a UV-bright AGN with either a patchy dusty torus or a sight-line cleared by feedback. Stars are obscured by a high dust covering fraction, likely due to a combination of the current episode of star formation and the compact size," the authors explain. Image Credit: Tripodi et al. 2025. NatComm*
"Altogether, this points to a highly compact system undergoing an episode of star formation with a high dust covering fraction in which a highly energetic AGN has cleared a sight-line in our direction," the authors explain. "We are witnessing the growth of an SMBH of 108 M⊙ in a very compact and massive galaxy (M ≃ 5 × 109 M⊙ in r* < 70 pc), unlike any other sources at the same redshift."
It's possible that CANUCS-LRD-z8.6 is more evolved than other LRDs that show less massive BHs and host galaxies. It may be on the path to becoming one of the brightest quasars at z = 6, instead of one of the less luminous AGNs the JWST has detected at these redshifts. If this is true, then the LRD could be an evolutionary link between early massive black holes and those quasars.
"This discovery is an exciting step in understanding the formation of the first supermassive black holes in the Universe,” explained Prof. Maruša Bradač, leader of the group at the University of Ljubljana, FMF. “The unexpected rapid growth of the black hole in this galaxy raises questions about the processes that allowed such massive objects to emerge so early. As we continue to analyse the data, we hope to find more galaxies like CANUCS-LRD-z8.6, which could provide us with even greater insights into the origins of black holes and galaxies."
There are many unanswered questions regarding LRD, and while these new observations are no doubt part of the way forward, it doesn't provide immediate answers. How does this discovery relate to the idea of black hole seeds? Do episodes of Super-Eddington accretion play a role? Even though it can't answer outstanding questions outright, its discovery places constraints on the eventual answers. "The discovery of CANUCS-LRD-z8.6, featuring one of the highest BH masses and the highest stellar mass at z > 8, provides essential constraints for simulations and theoretical models," the authors write.
The team of researchers aren't yet finished with CANUCS-LRD-z8.6. They're planning more observations not only with the JWST, but with the Atacama Large Millimetre/submillimetre Array (ALMA). ALMA is designed to see cold gas in the system, and those observations will refine and broaden the understanding of the LRD. Other researchers will also likely get involved, and the study of this fascinating ancient galaxy could help us answer important questions about the early Universe, especially how galaxies and black holes evolved together in the first few hundred million years after the Big Bang.
