Astrophysicists from the University of Copenhagen have discovered that the enigmatic “little red dots” visible in images of the early universe are rapidly growing black holes shrouded in ionized gas. This groundbreaking finding offers significant insights into the formation of supermassive black holes after the Big Bang.
The small red dot is a young supermassive black hole encased in a dense ionized cocoon. Image credits: NASA / ESA / CSA / Webb / Rusakov et al., doi: 10.1038/s41586-025-09900-4.
Since the launch of the NASA/ESA/CSA James Webb Space Telescope in 2021, astronomers globally have been studying the red spots that appear in regions of the sky corresponding to the universe just a few hundred million years after the Big Bang.
Initial interpretations ranged from unusually massive early galaxies to unique astrophysical phenomena that challenged existing formation models.
However, after two years of extensive analysis, Professor Darach Watson and his team from the University of Copenhagen have confirmed that these points represent young black holes surrounded by a thick cocoon of ionized gas.
As these black holes consume surrounding matter, the resulting heat emits powerful radiation that penetrates the gas, creating a striking red glow captured by Webb’s advanced infrared camera.
“The little red dot is a young black hole, approximately 100 times less massive than previously estimated, encased in a gas cocoon and actively consuming gas to expand,” stated Professor Watson.
“This process generates substantial heat, illuminating the cocoon.”
“The radiation that filters through the cocoon provides these tiny red dots with their distinctive color.”
“These black holes are significantly smaller than previously thought, so there’s no need to introduce entirely new phenomena to explain them.”
Despite being the smallest black holes ever detected, these objects still weigh up to 10 million times more than the Sun and measure millions of kilometers in diameter, shedding light on how black holes accelerated their growth during the early universe.
Black holes typically operate inefficiently, as only a small fraction of the gas they attract crosses the event horizon. Much is blown back into space as high-energy outflows.
However, during this early phase, the surrounding gas cocoon serves as both a fuel source and a spotlight, enabling astronomers to observe a black hole in intense growth like never before.
This discovery is crucial for understanding how supermassive black holes, such as the one at the center of the Milky Way, grew so quickly in the universe’s first billion years.
“We observed a young black hole in a growth spurt at a stage never documented before,” Professor Watson remarked.
“The gas-dense cocoon around them supplies the rapid growth fuel they require.”
For more details, see the findings featured in this week’s edition of Nature.
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V. Rusakov et al. 2026. A small red dot like a young supermassive black hole inside a dense ionized cocoon. Nature 649, 574-579; doi: 10.1038/s41586-025-09900-4
Source: www.sci.news
