For the past few years, astronomers have been grappling with a cosmic mystery first revealed by NASA’s James Webb Space Telescope (JWST). Practically everywhere JWST looked into the distant depths of the sky, probing the time when our universe was only several hundred million years old, it saw something hard to explain: bright, strangely dense spots that were dark red in color. Spots were ubiquitous in the scenes of this early era. But then, about two billion years into the history of the universe, they disappeared from JWST’s view just as quickly as they had appeared.
Further investigation of these “little red dots” (LRDs) deepened the mystery. They looked far more massive and mature than the early galaxies shining from swarms of newborn stars, yet they were not blasting out the X-ray and radio waves that are the hallmark of supermassive black holes that feed on gas and dust. For some time, LRDs were considered cosmological breakers because they rejected practically every expectation set by well-established theories.
However, an answer may now be at hand. Published on Wednesday in Nature and derived from deeper, more time-consuming JWST observations of a dozen LRDs, which split their light into its component colors, or spectra, a new study Strengthens the case that these objects are indeed massive, expanding black holes. If so, the seemingly missing X-ray and radio bursts from these objects would be hidden behind a dense cocoon of ionized gas. Feeding black holes typically emit abundant ultraviolet radiation from white-hot disks of material that pile up around their insatiable claws. For LRDs, that ultraviolet light will filter through their cocoon, coming out as visible light and creating the distinctive red color. The LRDs will naturally disappear as the growing, gas-gurgling black hole hollows out their cocoon.
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If confirmed by additional data, this picture could mean that LRDs represent a new, previously unknown stage in the lives of supermassive black holes – and the youngest stage we have ever seen them.
“This cocoon makes these black holes red and blocks most of their radiation from escaping and explains why they look so compact,” says Vadim Rusakov, an astronomer at the University of Manchester in England and lead author of the study. In this scenario, in addition to hiding the black hole, the cocoons also make these objects appear heavier because the electrons from their envelope of ionized gas scatter the outgoing light in a way that mimics the light we see from more massive objects. Correcting for this effect, the research team calculated that the black holes hidden within the LRD are between 100,000 and 10 million solar masses in size—relative peeps compared to more mature supermassive black holes, which can tip the cosmic scales at billions of solar masses. “The detailed physics inside the gas cocoon is still an open area of research,” says Rusakov. “But now we think the main mystery has been solved: LRDs almost certainly host accreting black holes.”
However, not all astronomers are certain that the matter is closed. Of the numerous LRDs observed with JWST, Nature The study examines only a dozen closely. It’s possible that further observation of many more LRDs may reveal that they are not all one type of object – perhaps some are cocooned black holes, as the study suggests, and others are completely different things.
Rodrigo Nemen, an astrophysicist at the University of São Paulo, who wrote along with a comment But Nature The study largely agrees with Rusakov and his team’s explanation. The team’s work is “a huge step forward” producing a model that is “beautiful and ties up a lot of loose ends,” he says. “The LRDs once demanded either impossibly efficient galaxy formation or massive black holes appearing out of nowhere in the young universe – either way, something was horribly wrong in our models.” But their estimated mass decreased Nature Study, any black hole within the LRD would be easier for existing models to account for.
These findings are not entirely surprising, says Rohan Naidu, an astrophysicist at the Massachusetts Institute of Technology, who also studies LRDs. On the same day in March 2025, a preprint version of Nature The study was posted online, along with preprints of two other investigations that focused on LRDs—One which was led by Naidu one more It was led by Anna de Graaff of the Center for Astrophysics at Harvard and the Smithsonian. All three papers presented complementary results that suggest LRDs are cocooned supermassive black holes. Additional work from theorists around the world has further corroborated this idea.
Like many of his colleagues, Naidu is now so confident in the explanation that he prefers to call the LRD a “black hole star” because of some of the associated physics. “They effectively radiate like giant stars,” he says, “although LRDs can be up to a trillion times more luminous.” “Instead of nuclear fusion capturing a ball of gas like our Sun, we have … a furiously fed black hole whose radiation powers this structure.”
Yet despite the emerging consensus, key questions remain unanswered.
The crux of the controversy, says Neyman, is how much ionized gas would be in a cocoon and thus how much electron scattering would interfere with the measurement of a latent black hole’s true mass. He says that interpreting the JWST’s spectral data is “extremely difficult”, in that even minor variations can significantly alter the resulting mass estimate – in theory, they would be skewed so much that the case for hidden black holes would be weakened.
But such an outcome seems unlikely, Rusakov says, given the multiple, independent lines of supporting evidence, as well as the lack of any other plausible mechanism that would allow all the various pieces of the LRD puzzle to fit together neatly. “Without ionized gas, the data means nothing,” he says.
And even if the LRD mystery were solved – and the current paradigm of cosmology was saved – many new questions would arise. “Can we find even smaller black holes (in the early universe) with JWST? Do they start small and grow, or are they born already quite large?”. Rusakov asks. “LRDs may be our best candidates to explore.”
