Mystery objects in the early universe may be black hole stars

Not everything in the universe is what it seems. Some things, like tiny red objects captured by NASA’s James Webb Space Telescope (JWST), might look like stars or galaxies. But new research suggests they could be something else entirely – something we’ve never seen before.

The objects, called “little red dots,” were first spotted when Webb returned its initial pictures in 2022. The dots appeared where young galaxies would be alone, 500 to 700 million years after the Big Bang. But they were too bright and too big to be galaxies that early in the universe. Something wasn’t adding up.

For a while, researchers thought they had discovered ancient, mature galaxies that somehow formed way faster than expected – so fast they started calling them “universe breakers.” But after digging deeper, a new idea started to form. Maybe these weren’t galaxies at all.

A star that’s hiding a black hole

In a recent study, scientists proposed a bold theory: the red dots might be something called a black hole star. Picture a huge sphere of gas that looks like a cold, low-energy star – but inside, it’s hiding a growing supermassive black hole.

Instead of getting its energy from fusion like a normal star, this object feeds off matter falling into the black hole at its core. That process generates energy and gives off light, creating the bright signal scientists saw.

“Basically, we looked at enough red dots until we saw one that had so much atmosphere that it couldn’t be explained as typical stars we’d expect from a galaxy,” said Joel Leja, an associate professor of astrophysics at Penn State.

“It’s an elegant answer really, because we thought it was a tiny galaxy full of many separate cold stars, but it’s actually, effectively, one gigantic, very cold star.”

Cold stars that shine strangely

Stars that are cold emit very little visible light. They glow mainly in the red or near-infrared part of the spectrum – a type of light our eyes can’t see. These stars are usually small and faint, which makes them hard to find.

But these red dots stood out. The light they gave off wasn’t from a hot, bright region like we usually see near black holes. Instead, it came from very cold gas, similar to what’s found around low-mass stars.

Webb was built to pick up exactly this kind of ancient, stretched-out infrared light. Its infrared sensors can see light that traveled across the universe for over 13 billion years. That makes it perfect for spotting objects from the very early days of the cosmos.

The most extreme red dot

Between January and December 2024, the team gathered spectra – a kind of light fingerprint – from 4,500 galaxies. Spectra can tell scientists how bright something is across different wavelengths, which helps them figure out what it’s made of and how massive it is.

One of these objects stood out. Nicknamed “The Cliff,” it turned out to be the most extreme of all the red dots. It was so far away that its light took about 11.9 billion years to reach Earth.

“The extreme properties of The Cliff forced us to go back to the drawing board, and come up with entirely new models,” said Anna de Graaff, a researcher for the Max Planck Institute for Astronomy.

Spectral analysis showed that The Cliff wasn’t made up of countless tiny stars. It was a single, massive object – a black hole pulling in gas so fast that it wrapped itself in a glowing shell of hydrogen.

Are black hole stars a missing link?

Black holes are found at the center of most galaxies. Some of them are enormous – millions or even billions of times more massive than our sun. But no one knows exactly how they got that big, or how they formed in the first place.

“No one’s ever really known why or where these gigantic black holes at the center of galaxies come from,” said Leja. “These black hole stars might be the first phase of formation for the black holes that we see in galaxies today – supermassive black holes in their little infancy stage.”

That idea could help solve a major puzzle in astronomy. If these red dots are actually black hole stars, then maybe they’re the missing link – the early-stage objects that grow into the supermassive black holes we see in today’s galaxies.

Following clues from the universe

The team plans to keep studying these black hole star candidates, especially by looking at how dense the gas is and how strong the light output is. That might help confirm whether they’re really seeing a new type of object.

“This is the best idea we have and really the first one that fits nearly all of the data, so now we need to flesh it out more,” said Leja.

“It’s okay to be wrong. The universe is much weirder than we can imagine and all we can do is follow its clues. There are still big surprises out there for us.”

The full study was published in the journal Astronomy and Astrophysics.

Image Credit: T. Müller/A. de Graaff/Max Planck Institute for Astronomy

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