Artist’s impression of a black hole star (not to scale). Mysterious tiny pinpoints of light discovered at the dawn of the universe may be giant spheres of hot gas that are so dense they look like the atmospheres of typical nuclear fusion-powered stars; however, instead of fusion, they are powered by supermassive black holes in their center that rapidly pull in matter, converting it into energy and giving off light. Credit: T. Müller/A. de Graaff/Max Planck Institute for Astronomy
Astronomers at Penn State have nicknamed the objects “universe breakers,” which may be unusual black hole atmospheres and could represent a missing link in the fast growth of supermassive black holes.
Small, faint red sources detected by NASA’s James Webb Space Telescope (JWST) are giving astronomers fresh clues about how galaxies formed in the early universe — and may point to a completely new category of cosmic object: a black hole consuming huge amounts of matter while emitting light.
When the telescope’s first data became available in 2022, an international collaboration that included researchers from Penn State identified puzzling “little red dots.” At first, the team proposed that these objects could be galaxies as developed as today’s Milky Way, which is about 13.6 billion years old, existing only 500 to 700 million years after the Big Bang.
Rethinking early galaxies
The researchers informally named the objects “universe breakers,” since they initially appeared to be galaxies far older and more evolved than expected in the early universe — a finding that would challenge long-held ideas of galaxy formation.
In a paper published on September 12, 2025, in Astronomy & Astrophysics, the team, which included astronomers and physicists from Penn State, proposed a different explanation. They argue the red dots are not galaxies at all but a previously unknown type of object known as a black hole star.
According to their analysis, the faint points of light may actually be enormous spheres of hot gas so compact that they resemble the atmospheres of ordinary stars fueled by nuclear fusion. In this case, however, the energy source is not fusion but supermassive black holes at their centers, which draw in matter at high speed, transform it into energy, and emit light.
One gigantic cold star
“Basically, we looked at enough red dots until we saw one that had so much atmosphere that it couldn’t be explained as typical stars we’d expect from a galaxy,” said Joel Leja, the Dr. Keiko Miwa Ross Mid-Career Associate Professor of Astrophysics at Penn State and co-author on the paper. “It’s an elegant answer really, because we thought it was a tiny galaxy full of many separate cold stars, but it’s actually, effectively, one gigantic, very cold star.”
Leja explained that cold stars give off only faint light because their surface temperatures are much lower than those of typical stars. Although the majority of stars in the universe fall into this low-mass, cooler category, they are often difficult to detect since their dim glow is overshadowed by the rarer but much brighter massive stars. Astronomers recognize cold stars by their emission in the red optical and near-infrared range, wavelengths of light that are no longer visible to the human eye. In contrast to the extremely hot gas usually found near supermassive black holes, which can reach millions of degrees Celsius, the light from these “red dot” black holes was dominated by very cold gas. According to the researchers, this emission closely resembled the atmospheres of low-mass, cold stars, based on the wavelengths detected.
Seeing back in time
The most powerful telescope in space, JWST was designed to see the genesis of the cosmos with infrared-sensing instruments capable of detecting light that was emitted by the most ancient stars and galaxies. Essentially, the telescope allows scientists to see back in time roughly 13.5 billion years, near the beginning of the universe as we know it, Leja explained.
From the moment the telescope turned on, researchers around the world began to spot “little red dots,” objects that appeared far more massive than galaxy models predicted. At first, Leja said, he and his colleagues thought the objects were mature galaxies, which tend to get redder as the stars within them age. But the objects were too bright to be explained — the stars would need to be packed in the galaxies with impossible density.
Extreme object named the cliff
“The night sky of such a galaxy would be dazzlingly bright,” said Bingjie Wang, now a NASA Hubble Fellow at Princeton University who worked on the paper as a postdoctoral researcher at Penn State. “If this interpretation holds, it implies that stars formed through extraordinary processes that have never been observed before.”
To better understand the mystery, the researchers needed spectra, a type of data that could provide information about how much light the objects emitted at different wavelengths. Between January and December 2024, the astronomers used nearly 60 hours of Webb time to obtain spectra from a total of 4,500 distant galaxies. It is one of the largest spectroscopic datasets yet obtained with the telescope.
In July 2024, the team spotted an object with a spectrum that indicated a huge amount of mass, making it the most extreme case of such an early and large object. The astronomers nicknamed the object in question “The Cliff,” flagging it as the most promising test case to investigate just what those “little red dots” were.
A fiery cocoon of gas
“The extreme properties of The Cliff forced us to go back to the drawing board, and come up with entirely new models,” said Anna de Graaff, a researcher for the Max Planck Institute for Astronomy and corresponding author on the paper, in a Max Planck Institute press release.
The object was so distant that its light took roughly 11.9 billion years to reach Earth. The spectra analysis of that light indicated it was actually a supermassive black hole, pulling in its surroundings at such a rate that it cocooned itself in a fiery ball of hydrogen gas. The light that Leja and his colleagues spotted was coming not from thick clusters of stars, but from one giant object.
Black holes at galaxy centers
Black holes are at the center of most galaxies, Leja explained. In some cases, those black holes are millions or even billions of times more massive than our solar system’s sun, pulling in nearby matter with such strength that it converts to energy and shines.
“No one’s ever really known why or where these gigantic black holes at the center of galaxies come from,” said Leja, who is also affiliated with Penn State’s Institute for Computational and Data Sciences. “These black hole stars might be the first phase of formation for the black holes that we see in galaxies today — supermassive black holes in their little infancy stage.”
He added that JWST has already found signs of high-mass black holes in the early universe. These new black hole star objects, which are essentially turbocharged mass-builders, could help explain the early evolution of the universe — and may be a welcome addition to current models. The team is planning future work to test this hypothesis by examining the density of gas and strength of these early black hole stars, Leja said.
Of course, the mysterious “little red dots” are great distance away in both time and space — and their small size makes it especially challenging to get a clear picture.
“This is the best idea we have and really the first one that fits nearly all of the data, so now we need to flesh it out more,” Leja said. “It’s okay to be wrong. The universe is much weirder than we can imagine and all we can do is follow its clues. There are still big surprises out there for us.”
Reference: “A remarkable ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a little red dot at z = 3.5” by Anna de Graaff, Hans-Walter Rix, Rohan P. Naidu, Ivo Labbé, Bingjie Wang, Joel Leja, Jorryt Matthee, Harley Katz, Jenny E. Greene, Raphael E. Hviding, Josephine Baggen, Rachel Bezanson, Leindert A. Boogaard, Gabriel Brammer, Pratika Dayal, Pieter van Dokkum, Andy D. Goulding, Michaela Hirschmann, Michael V. Maseda, Ian McConachie, Tim B. Miller, Erica Nelson, Pascal A. Oesch, David J. Setton, Irene Shivaei, Andrea Weibel, Katherine E. Whitaker and Christina C. Williams, 10 September 2025, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202554681
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