Since the James Webb Space Telescope (JWST) began scientific operations, astronomers have been intrigued by strange red dots appearing in its images of the distant universe. Scientists from the University of Copenhagen have now identified what these objects are, uncovering extreme cosmic activity hidden inside dense clouds of ionized gas. Their findings were published in Nature on January 14.
When James Webb captured its first images in December 2021 from a distance of about 1.5 million kilometers from Earth, researchers quickly noticed something unexpected. Scattered among stars and galaxies were small, unexplained red points of light that did not fit existing models of the early universe.
A Cosmic Mystery in the Early Universe
These objects, nicknamed “little red dots,” appear during a period when the universe was only a few hundred million years old. Roughly a billion years later, they seem to vanish from view. Their brief appearance raised a major question: what exactly were these glowing red sources?
One early idea suggested they were massive galaxies bright enough to be detected across 13 billion years of cosmic history. However, that explanation conflicted with what scientists know about galaxy formation. Such large galaxies should not have existed so soon after the Big Bang, as they require much more time to develop.
Black Holes Hidden in Gas Cocoons
After analyzing Webb’s data for two years, researchers at the Niels Bohr Institute’s Cosmic Dawn Centre reached a different conclusion. The red dots are powered by black holes, the most extreme objects known in the universe. These observations offer a rare look at how the first black holes formed and began to grow.
“The little red dots are young black holes, a hundred times less massive than previously believed, enshrouded in a cocoon of gas, which they are consuming in order to grow larger. This process generates enormous heat, which shines through the cocoon. This radiation through the cocoon is what gives little red dots their unique red color,” says Professor Darach Watson, one of the lead authors of the study.
‘”They are far less massive than people previously believed, so we do not need to invoke completely new types of events to explain them.”
The significance of the discovery placed the Cosmic Dawn Centre team on the front page of Nature, one of the world’s most influential scientific journals.
Why Black Holes Are “Messy Eaters”
Astronomers have now identified hundreds of these little red dots, all of them young black holes. While they are among the smallest black holes ever observed, they are still enormous by everyday standards, weighing up to 10 million times the mass of the Sun and stretching about ten million km across.
Black holes grow by pulling in nearby gas and dust. Because their event horizons are relatively small, material falling inward becomes extremely hot and bright before crossing the point of no return. This process releases more energy than almost any other known phenomenon in the universe. The intense radiation pushes much of the incoming material back outward instead of allowing it to be swallowed.
“When gas falls towards a black hole, it spirals down into a kind of disk or funnel towards surface of the black hole. It ends up going so fast and is squeezed so densely that it generates temperatures of millions of degrees and lights up brightly. But only a very small amount of the gas is swallowed by the black hole. Most of it is blown back out from the poles as the black hole rotates. That’s why we call black holes ‘messy eaters’,” explains Darach Watson.
Solving the Puzzle of Rapid Black Hole Growth
Every large galaxy, including the Milky Way, contains a supermassive black hole at its center. The one in our galaxy has a mass about four million times that of the Sun. Despite their importance, scientists are still trying to understand how these enormous objects formed so early in cosmic history.
The new findings help explain how supermassive black holes could already exist just 700 million years after the Big Bang, some reaching masses billions of times greater than the Sun. Observing these young black holes during an intense growth phase fills in a missing chapter of cosmic evolution.
“We have captured the young black holes in the middle of their growth spurt at a stage that we have not observed before. The dense cocoon of gas around them provides the fuel they need to grow very quickly,” says Darach Watson.