Early Universe’s ‘Little Red Dots’ Are Young Supermassive Black Holes, Astrophysicists Say
Astrophysicists at the University of Copenhagen show that enigmatic “little red dots” – red sources scattered across images of the early Universe – are fast-growing black holes enveloped in ionized gas, offering new insight into the formation of supermassive black holes after the Big Bang.
The little red dots are young supermassive black holes in dense ionized cocoons. Image credit: NASA / ESA / CSA / Webb / Rusakov and others., doi: 10.1038/s41586-025-09900-4.
Since the launch of the NASA/ESA/CSA James Webb Space Telescope in 2021, astronomers around the world have looked into the nature of the red dots visible in regions of the sky corresponding to the Universe only a few hundred million years old.
Early interpretations ranged from the first unusually massive galaxies to exotic astrophysical phenomena that challenged existing models of formation.
But after two years of careful analysis, Professor Darach Watson of the University of Copenhagen and his colleagues show that these dots are young black holes enveloped in dense cocoons of ionized gas.
These cocoons heat up as the black holes engulf surrounding matter, emitting intense radiation that is filtered through the gas and appears as a distinctive red glow captured by Webb’s infrared cameras.
“The little red dots are young black holes, a hundred times less massive than we thought, enveloped in a cocoon of gas, which they consume to grow,” explained Professor Watson.
“This process generates enormous heat which shines through the cocoon. »
“It is this radiation through the cocoon that gives the little red dots their unique red color.”
“They are much less massive than previously believed, so we don’t need to invoke completely new types of events to explain them.”
Although they are among the smallest black holes ever detected, these objects still pack a punch: weighing up to 10 million times more than the Sun and stretching millions of kilometers across, they reveal how black holes in the early Universe could have accelerated their growth.
Black holes are inefficient eaters: only a fraction of the gas sucked in crosses the event horizon, while much of it is returned to space as high-energy outflows.
But during this first phase, the gas cocoons surrounding them act as both fuel and searchlight, allowing astronomers to observe the black holes in an intense growth spurt never before seen.
These results offer a crucial piece in the puzzle of how supermassive black holes – like the one at the center of the Milky Way – could have grown so quickly during the first billion years of the Universe.
“We captured the young black holes in the middle of their growth spurt, at a stage we had never observed before,” Professor Watson said.
“The dense cocoon of gas that surrounds them provides the fuel they need to grow very quickly. »
The results appear this week in the journal Nature.
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V. Rusakov and others. 2026. Small red dots like young supermassive black holes in dense ionized cocoons. Nature 649, 574-579; doi: 10.1038/s41586-025-09900-4
