When the James Webb Space Telescope looks deep into the Universe, some of the objects it finds appear as small, red dots. Astronomers call them little red dots (LRDs), and they have become one of the telescope’s more intriguing discoveries.
Now, an international team of astronomers has found an unusual object that may help explain what at least some of these red dots actually are: unusually young and rapidly growing black holes surrounded by an enormous amount of dense gas.
The astronomers spotted the object in question in the study from when the universe was just around 660 million years old. Put another way, the light from this object has travelled for more than 13 billion years before reaching the earth, which the Webb telescope orbits.
The researchers’ observations suggest that almost all the light coming from the object is produced by a supermassive black hole. They were published in Nature on August 12.
Astronomers have generally thought that the red colour of LRDs is due to dust. This is because dust absorbs blue light more readily than red light, so more red light reaches the observer.
However, the team found the object to be telling a different story. Specifically, they found that its colour could instead be explained by a colossal cocoon of gas surrounding the black hole.
An unexpected break
The team first spotted the object in images taken by the Webb telescope because it was exceptionally red in colour. It appeared in some of the telescope’s infrared filters but virtually disappeared at shorter wavelengths.
The researchers then used one of Webb’s instruments to split its light into its spectrum — its various wavelengths. And this spectrum contained something extraordinary: a very large Balmer break. This is a gap in the spectrum that occurs because hydrogen is absorbing light at those wavelengths. Astronomers are used to seeing this break in light coming from stars, but it is still not so big.
The Balmer break in the light from the object suggested that the light was passing through a large and turbulent quantity of hydrogen gas.
According to the astronomers’ model, it would have to have around 100 billion particles per cubic centimetre, extend to several million kilometres around the black hole, and move at hundreds of kilometres per second.
(Aside: Even air at sea level on the earth contains around 25 billion particles per cubic centimetre — meaning the hydrogen cocoon is around 250 million times less dense than ordinary air! The cocoon is still exceptional because of the fact that this relatively thin gas is still spread across a large distance while also being concentrated around a violent black hole, and being dense enough to distort the light passing through it.)
The black hole is actively feeding on matter. As material falls towards it, it forms a hot, bright accretion disk and releases enormous amounts of radiation. That radiation escapes into space after passing through the surrounding gas. And to an observer on the earth, that light looks redder.
Growing so fast
In an independent commentary accompanying the paper, astronomers Dominik Schleicher of the Sapienza University of Rome and Rodrigo Herrera-Camus of the University of Concepción, Chile, wrote that the discovery could be important for scientists to understand other LRDs.
One notable implication is that if some of these black holes appear redder due to gas rather than dust, their masses could be substantially lower — up to a 100-times — than astronomers have previously estimated.
A study published in Nature on May 27 provided an important piece of the puzzle from a different direction. Astronomers studied a different LRD that existed when the universe was around 700 million years old. By measuring how gas was rotating around the object, they were able to estimate its mass: about 50 million-times that of the sun — which is high.
But equally remarkably, its host galaxy had less stellar mass than the black hole’s mass, suggesting that at least some of the universe’s early black holes may have grown much faster than their surrounding galaxies had accumulated most of their stars.
The new study (from August 12) also offered a clue to how this could happen. For some years now, astronomers have not been able to make sense of how very massive black holes could exist when the universe was so young, less than a billion years old. If a black hole formed with the mass of a star, they wouldn’t be able to grow at the conventional rate to become supermassive so quickly.
One possibility that the new study buttresses is that these black holes didn’t grow at the conventional rate. Astronomers had previously proposed that when a black hole is surrounded by a dense cloud of gas, it could grow faster than expected — and the hydrogen cocoon surrounding the newfound black hole presents just such a scenario.
More complicated explanation
The team’s model also found that the light from the object had a combination of properties that favoured the hydrogen surrounding the black hole rather than being far from the black hole but lying along the line of sight.
That said, the study’s authors also stressed that their observation does not establish the idea conclusively. For one, the exact mechanism by which the black hole and its dense envelope formed remains an open question.
There is another intriguing detail. According to the study, the object appears to be in a relatively small galaxy while a considerably more massive galaxy is located nearby. The two galaxies are also expected to merge in roughly 100 million years. The researchers pointed out that if the black hole’s light and the neighbouring galaxy were eventually seen together, the combined object would look remarkably similar to a typical LRD.
For decades, astronomers have used dust as the obvious explanation when distant objects appear unusually red. The Webb Space Telescope, which NASA launched in late 2021, is now showing that the explanation can be more complicated.
Schleicher and Herrera-Camus also noted that such gas-rich environments could help explain other peculiar properties of LRDs, including their surprisingly weak X-ray emissions. Future radio telescopes may also be able to probe the electrons moving through these environments and provide information that Webb is not designed to.
Published – August 17, 2026 01:15 pm IST
