Astronomers have solved the mystery of the strange red dots spotted in images from the James Webb Space Telescope, identifying them as young black holes growing rapidly within dense gas clouds. This discovery, led by researchers from the University of Copenhagen, explains how supermassive black holes could form so early in the universe's history. The findings were published in Nature on January 14.
Since the James Webb Space Telescope (JWST) began capturing images in December 2021 from about 1.5 million kilometers from Earth, scientists have puzzled over small, unexplained red points of light amid stars and galaxies in the distant universe. These "little red dots" appear during the universe's youth, when it was just a few hundred million years old, and seem to disappear roughly a billion years later.
Initial theories proposed they were massive galaxies visible across 13 billion years of cosmic history, but this clashed with known timelines for galaxy formation, which require more time post-Big Bang. After two years of analyzing JWST data, a team from the Niels Bohr Institute's Cosmic Dawn Centre at the University of Copenhagen offered a breakthrough explanation: the dots are young black holes, far smaller than previously thought, enveloped in cocoons of ionized gas.
"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," said Professor Darach Watson, a lead author of the study. "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."
These black holes, weighing up to 10 million times the Sun's mass, grow by accreting gas and dust, which spirals into hot, bright disks before much of it is ejected due to intense radiation. Watson described the process: "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'."
The observation captures these black holes in a rapid growth phase around 700 million years after the Big Bang, providing clues to the origins of supermassive black holes at galaxy centers, like the Milky Way's four-million-solar-mass giant. "We have captured the young black holes in the middle of their growth spurt at a stage that we have not observed before," Watson noted. "The dense cocoon of gas around them provides the fuel they need to grow very quickly."
Hundreds of such dots have now been identified, highlighting a violent, messy era in cosmic evolution.