Little red dots in the early universe may be a little less mysterious

Astronomers now have stronger evidence that mysterious "little red dots" found in the early universe could come from black holes wrapped in thick clouds of gas disguising their light.

Little red dots have puzzled astronomers since their discovery in 2022. Initially, some researchers thought they "broke cosmology," unsure how unusually mature galaxies could have formed so fast after the Big Bang, forcing scientists to rethink their understanding of the dawn of time. 

NASA's James Webb Space Telescope has taken a deep look at one of these strange objects, a distant source called GLIMPSE-17775. It appears so small, so compact, and so red that it defies standard classification. By studying the space object's light, a team of researchers teased out more than 40 distinct chemical features. Taken together, they gave scientists a model for what the environment inside the object must look like. 

The verdict: GLIMPSE-17775 behaves like a voracious supermassive black hole, gobbling up a meal while encased in layers of gas. The team's study was published in The Astrophysical Journal. 

"Everything fits, nothing is broken, and I think that makes the puzzle that is our universe even better," said Vasily Kokorev, lead author of the paper, in a statement. "Looking ahead, I'm eager to dive deeper and learn about what is powering the central engines of little red dots." 

Earlier studies suggested perhaps these little red dots were ordinary galaxies, just heavily altered in appearance by surrounding dust. Others proposed something more radical: supermassive black holes feeding inside dense balls of gas. The concept became known as a "black hole star." 

Mashable Light Speed

Scientists based the idea on broad clues, like the objects' compact size and unusual hydrogen patterns. But those alone couldn't tell them what physical processes were occurring to shape their light.

Kokorev's team created a spectrum of GLIMPSE-17775, which existed about 1.8 billion years after the Big Bang, by splitting its light into its component colors. The technique can reveal the presence and absence of different elements and conditions. These new observations allowed them to test the idea of a black hole star from several different angles. 

One of the clearest clues came from the way the little red dot's light behaves. Instead of traveling directly into space, it appears to have ricocheted. That only happens in a dense cocoon of gas — far denser than what astronomers would see in an ordinary galaxy. 

At the center of that gas shell likely sits an actively feeding black hole, aka a quasar, according to the paper. As matter falls toward it, it releases energy. But instead of making a clean getaway, much of that energy gets absorbed and recycled by the surrounding gas. 

That process would naturally explain why the object appears very red and very compact. The gas changes the light before it ever reaches us.

"When we saw the spectrum for the first time, it was like having all the pieces of a puzzle scattered on the floor," said Kokorev, an astrophysicist at the University of Texas at Austin. "Maybe a few pieces looked like nothing at first, but then a couple of them came together, and we realized that there was something there."

The study also discusses the masses of these objects. Because earlier estimates relied on measuring how fast gas moves around the black hole, those figures may be unreliable, according to the paper. In an environment of dense gas such as this, the light could become extremely distorted before it reaches telescopes.  

If that's the case, then some early-universe black holes may be smaller than they seem — just growing very quickly and shrouded in gas. That could resolve one of the biggest problems with little red dots: how something so early in cosmic history could grow to be so seemingly large.