The James Webb Telescope Is Changing Astronomers’ Understanding of the Ancient Cosmos - WIRED

When Charlotte Mason ponders cosmic mysteries, she likes to doodle. “I am quite a visual person,” she said. “I usually draw a lot of pictures trying to understand what’s going on.”

Mason, an astrophysicist at the Cosmic Dawn Center in Copenhagen, has lately been filling pages with sketches of “little red dots,” perplexing objects discovered by the hundreds in images from the James Webb Space Telescope (JWST). Little red dots were never seen before the telescope came online in 2022. But we now know that they started to appear in significant numbers roughly 650 million years after the Big Bang.

These dots are just one of the thrilling mysteries that have emerged from JWST’s observations of the early universe. Others include black holes that seem impossibly large for their age, as well as ancient galaxies that defy what we thought we knew about the first billion years after the Big Bang. At first, scientists were astounded: The universe revealed by JWST simply didn’t square with our understanding of astrophysics. Now, a wave of new theories offers tantalizing solutions—but which ones portray reality is an open question.

Recent ideas suggest that little red dots could be black holes cocooned in thick gas, possibly representing a completely new type of object called a black hole star, in which the tight shroud of gas emits light like a stellar atmosphere.

“This would be my black hole,” Mason said, drawing a small circle and filling it in. “I might put a disk on it, because we think that’s where some of the emission comes from.” She slashed a line through the circle’s center. “Then the kind of naïve picture is just this dense gas cloud around the black hole.” She drew a larger circle surrounding the object.

But Mason thinks there may be more to these cosmic enigmas. She and colleagues recently analyzed the spectrum of light emitted by one little red dot. If the dense-cloud picture is correct, then some of the light should have been altered from passing through the gas—but that’s not what they saw.

A sampling of the enigmatic little red dots that JWST has spotted in the early universe.

“Now what do I do? Start again. But now if I make my gas clumpy,” Mason said, drawing a new diagram with holes in the clouds surrounding the black hole, “I should be able to get [a signal] that looks closer.”

All around the world, researchers like Mason are eagerly piecing together JWST’s glimpses of the ancient cosmos to create a clearer picture of our universe’s beginnings. And like the photons that travel billions of light-years to reach us, new fragments are constantly falling into place.

The Universe’s Bottomless Pits

The story of black holes has become more complicated thanks to JWST, which keeps spotting ancient black holes that are too big to explain with established theories—much too big.

Shortly after the Big Bang, the universe was largely featureless and smooth. Then, just a few hundred million years later, “we already see billion-sun black holes growing,” said Jenny Greene, an astrophysicist at Princeton University. “In order to get them that big so quickly, you have to do some gymnastics.”

Scientists look at two key factors that influence a black hole’s size: how massive a black hole “seed” was when it originated, and how quickly these seeds grew after that. But it’s hard to explain how black holes either formed already big enough or grew fast enough to reach a billion times the mass of the sun in early cosmic times.

In the modern universe, black holes form when the core of a massive star runs out of fuel and collapses. Considering the first stars were quite massive, they could have left behind black hole seeds of up to about 100 solar masses, Greene said.

“We know that happens, but it’s really, really hard to get them to a billion so quickly,” she said. “You really have to force-feed them.”

Scientists have historically believed there’s a hard limit to how fast black holes can grow. As material falls toward the black hole, it gets hot as it spins around like water going down a drain. The radiation that this “accretion disk” produces pushes back against more stuff flying in, preventing the black hole from consuming more. This intake limit, called the Eddington limit, should make it impossible for black holes to grow tens of millions of times larger in the time available.