Astronomers debate strange objects called ‘little red dots’: NPR

Of all the mysteries that the massive James Webb Space Telescope has discovered so far in the early universe, one of the strangest concerns the objects that astronomers now call “little red dots.”

As their nickname suggests, these celestial objects appear compact, much smaller than our galaxy, the Milky Way. And their color is reddish, although their light signatures are also unusual in ways that astronomers have struggled to explain.

Now, at an American Astronomical Society conference this week in Maryland, astronomers say they have examined public data from the James Webb Space Telescope (JWST) to collect hundreds of examples of tiny dots red.

Their study shows that these cosmic oddities appear to be a common but fleeting feature of the early universe.

“Essentially, they all existed when the universe was a billion years old or less, and then they died out,” says Dale Kocevski, an astrophysicist at Colby College.

They may appear to disappear only because their appearance changes, he says, and “it could be that we’re seeing the cores of today’s massive galaxies form.”

The large galaxies that exist today almost all appear to have a supermassive black hole at their center, he notes. A subsample of small red dots that the researchers examined in more detail showed light signatures indicating that hot gas was spiraling downward into a growing black hole.

This could mean that the little red dots are “a potential building block, or perhaps the first step, in producing the galaxies and black holes we see today,” Kocevski says.

Break the universe

The massive $10 billion JWST is about a million miles from Earth and is capable of detecting extremely faint objects that the Hubble Space Telescope and ground-based telescopes have never seen .

When the little red dots first appeared in some of the early JWST observations, in December 2022, it was a surprise.

These faint objects are so distant that the light must travel for billions of years before it is finally detected by the telescope, meaning the light reveals how the universe appeared in its earliest stages of development.

The small, bright red dots initially looked like massive galaxies emitting dust-reddened starlight, but no one could understand how galaxies the size of the Milky Way could have formed so quickly, so soon after the Big Bang. .

People started talking “about how JWST was breaking existing theories about how the universe formed,” Kocevski says, “because these things were too massive, too early in the history of the universe.”

In early 2023, however, he and some colleagues examined a small red dot and detected light signatures indicating rapid rotation of gas in a black hole.

So they wondered whether it could be that the light from the small red dots was coming from both a growing black hole and stars in a small host galaxy, rather than from the stars alone.

“They may not be such massive galaxies,” says Kocevski.

He and his colleagues wanted to see if other small red dots bore signs of a black hole hidden inside. So they searched public data, looking for as many objects with the specific characteristics of the little red dots as they could find.

Examination of 341 of them revealed that these objects mostly appeared about 600 million years after the Big Bang and then declined, disappearing about 1.5 billion years ago.

Hotly debated

A subset of a few dozen small red dots had additional data, 80 percent of which showed the same signs of gas spiraling into a black hole, Kocevski says.

“So it seems like there’s a good chance that these are actively accumulating supermassive black holes,” he says. “What’s surprising is that they’re really, really common. They’re a lot more common than we would have expected.”

Yet some astronomers continue to believe that the small red dots are actually massive galaxies, he says.

The small red dots do not glow in X-ray light, which would normally be visible from black holes. However, gases may obscure this form of light.

“It’s been a very, very healthy academic debate about what’s going on with these things,” he says. “It’s exciting because you rarely find a population of objects where you say, ‘I just don’t know what’s going on here.’ “