Little red dots' may be pulsating monster stars that created early-universe black holes

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Add as preferred source Astronomers have speculated about the mysterious "little red dots" seen through the James Webb Space Telescope's images of the early universe: They could be galaxies, black holes, quasi-stars, starbursts ... or something else entirely.

Now, in a new study, researchers show that a particular type of star, called a supermassive star, can account for the LRDs' surprising characteristics, including their unusual spectra, compact appearance in the sky and abundance of nitrogen.

"To my knowledge, it is the first model that can explain so many of the observed properties at once, from the spectra to the morphology to the chemical signatures," said Devesh Nandal of the Harvard College Observatory, part of the Center for Astrophysics. "Even competing scenarios are now invoking supermassive stars as the central engine."

The LRDs are compact, red and extremely bright sources of light, and whatever is emitting the light existed when the universe was less than a billion years old. Their spectrum of light shows hydrogen occurring in ways that current astronomical models of young galaxies or ordinary active galactic nuclei can't explain.

But many observed LRDs don't have the strong X-ray or radio emission that astronomers would expect from a growing supermassive black hole.

"Little red dots are mysterious because they combine clues that do not usually fit together," said Nandal. "They seem to be telling us that something very luminous is hidden inside dense gas."

In earlier work published in The Astrophysical Journal , Nandal and collaborators showed that monster stars with masses around 100,000 times that of the sun can reproduce key spectra very much like LRDs, including unusual hydrogen patterns.

Their new study published in The Astrophysical Journal Letters looks at whether those stars can also create the dense "cocoons" of gas that make LRDs look so compact in James Webb images.

The researchers tracked the lifespans and evolution of some known monster stars and analyzed how they appear through our telescopes, how they blink and how they lose mass. They found that these stars don't lose mass late in their lives like many stars do. Instead, they undergo discrete, powerful pulsation episodes that the researchers call "strange-mode." This unusual behavior ejects shell-like shapes of gas.

"The spectrum and the morphology are two sides of the same physical problem," said Nandal. "The spectrum tells us what kind of source is producing the light and how that light is processed, while the shape tells us where the surrounding material is and how compact it must be."

Based on their models, the researchers show that a single supermassive star can create both the spectral signatures and the compact gas shell seen in LRDs.

The researchers note that ejected material is mainly hydrogen and helium but also contains nitrogen. Observations of LRDs are beginning to reveal similar nitrogen-rich spectra, which are another piece of evidence for their giant star theory.

After its last ejection, these stars continue to evolve until they undergo direct collapse, forming a seed of a supermassive black hole.

"What I find most fascinating is that this result brings together many independent clues in one physical picture," said Nandal.

The team's next goal is to turn these properties into full predictions for the detailed spectra of LRDs so that James Webb observations can directly test their theory.

Devesh Nandal et al, Supermassive Stars Match the Spectral Signatures of JWST's Little Red Dots, The Astrophysical Journal (2026). DOI: 10.3847/1538-4357/ae32f3

Devesh Nandal et al, Pulsational Mass Loss from Supermassive Stars Creates the Compact Shells of Little Red Dots, The Astrophysical Journal Letters (2026). DOI: 10.3847/2041-8213/ae82f3

Journal information: Astrophysical Journal Letters , Astrophysical Journal

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