The ‘Beautiful Confusion’ of the First Billion Years Comes Into View

Susan Kassin, an astronomer at the Space Telescope Science Institute, showed images from previous observatories compared to JWST’s. It was like having the optometrist flip a lens so that the last lines on an eye chart come into focus. “Thank you, Webb — it’s a $10 billion difference,” she said. People chuckled and nodded.

JWST is singular in its ability to see the young cosmos, which has drifted far away from us in both space and time. Its infrared sensors, its ultracold location in space, and its sunshield — which blocks the light of the sun, moon and Earth — are uniquely suited to resolve the first galaxies and their stars. These objects are too faint and at the wrong wavelengths to be seen by previous observatories, like the Hubble Space Telescope.

For astronomers, the vibe is collegial. Many presentations at the KITP conference included pleas for collaborators and partners in brainstorming.

“It was crazy competitive when the first data dropped. Now it is about coming up with ideas,” said Caitlin Casey of the University of Texas, Austin. “There is a firehose of data, and everyone has enough.”

The astrophysicist Rachel Somerville, who co-organized the meeting, said the community is scrambling to absorb both JWST’s data and its implications. Observers see things that are not explained in current theories about the evolution of the young cosmos.

“Many presentations showed that there is a tension between theory and observation,” said Fabio Pacucci of Harvard University, in one example of a cosmic understatement. To punctuate the confusion astronomers feel about this once-in-a-lifetime telescope upending what we know of the young universe, he flashed up a tongue-in-cheek slide: a cartoon of a dog sitting at a table sipping coffee while its house is in flames, captioned “This is fine.”

The Biggest and the Brightest

Astronomers kept referring to one of the most consequential galaxies seen so far, an unexpectedly bright smear of light called, dryly, JADES-GS-z14-0. Hainline, at the University of Arizona, is part of the team that discovered it with JWST and confirmed its distance in May 2024. It is the earliest known galaxy, knocking down the previous record holder, which was found by the same team in 2023.

At the time the galaxy shone forth, sound waves from the tremendous clap that started the universe were still ringing through the void. The first stars had been born in a cataclysmic baby boom, and some had already died. The dark hearts of black holes lurked, too — regions of space where gravity is so strong that not even light can escape. And there was this cluster of stars, resolved as a fuzzy scorpion shape in JWST filters. Two instruments on JWST were able to distinguish JADES-GS-z14-0’s brightness and its distance from Earth. Because of the accelerating expansion of the universe, objects at great distances are very far back in time. Astronomers can tell their ages based on the stretching of their light into longer wavelengths, known as redshift. Based on the most recent measurements, the galaxy was determined to lie at a redshift of 14.18, which means we see it as it appeared 300 million years after the Big Bang — when the universe was about 2% of its current age.

Initially, astronomers speculated that such huge, bright things so early in the universe were at odds with the prevailing theoretical model of the cosmos. But people have softened on that claim. Our best model of the universe — a set of equations describing the evolution of matter and radiation along with dark energy and dark matter — is not dead yet.

“There was a lot of sensationalism” in JWST’s early days, said Alice Shapley of the University of California, Los Angeles. “There is no need for that. The data are so beautiful; let’s just study the universe we have.”

Astrophysicists are coalescing around three star-based theories for how galaxies grew so bright so fast. One holds that stars during the cosmic dawn were very different from stars today. The stars in JADES-GS-z14-0, for instance, might be ultrabright but not actually very massive. While this seems plausible, it is also tricky for theoretical modelers to deal with. The correlation between a star’s brightness and its mass is a key value entered into computer simulations. If this value — known as the initial mass function, or IMF — was different in the early universe, then researchers would have to rewrite their simulations to be able to accommodate an IMF that changes over time.

But nature doesn’t care about our computing issues, and a changing IMF is, in principle, one of the most logical ways to make sense of what we see. “The IMF is truly the house of cards on which we build everything. There are many reasons to believe it is quite different at very high redshift,” Casey said.

Another theory holds that the extra-bright early galaxies happened to be undergoing furious bursts of star formation. Over 10 million or 100 million years, galactic brightness could vary by a factor of 100 as star formation ramped up and down. That’s like a candle turning into a floodlight in the span of a few seconds. Relatedly, during these busy spells, supernova explosions might have made things look brighter than they would otherwise appear.

The third theory suggests that star formation was way more efficient then than now. In a typical galaxy today, a small fraction of the gas is forged into stars; the Milky Way builds between two and six sun-size stars a year. But maybe the smallness and compactness of the early universe made it a better stellar factory. Some calculations suggest an almost 100% rate of conversion from gas to star, meaning fast and furious stellar birth, said Pratika Dayal of the University of Groningen in the Netherlands.

All these alterations to existing theory come with side effects, like changes in how much dust there should be and puzzles about how stellar baby booms settled down. And they’re not even the only ideas out there. Andrea Ferrara, a cosmologist at the Scuola Normale Superiore in Pisa, Italy, showed his colleagues in Santa Barbara a new model that tries to explain the bright early galaxies by changing the amount of dust within them, which would typically block starlight. His model assumes that more dust used to be blown away by stellar winds. “Reducing dust attenuation is my favorite hypothesis, even though I am totally open to having the other two,” he told attendees. But, he acknowledged, his calculations might not hold up at a redshift of 14, meaning they might not work for galaxies like JADES-GS-z14-0.

“So please don’t discover other galaxies,” he concluded, to laughter.

Big Black Holes

Star-related theories are not the only ideas. Some astrophysicists point to active supermassive black holes, which they say might heat surrounding gas and cause galaxies like JADES-GS-z14-0 to appear extremely bright.

In a series of papers published in May, the JADES team argues that the galaxy is starry, and that its brightness cannot be explained by black holes. But other galaxies do have such dark hearts. We know supermassive black holes weighing hundreds of millions or billions of suns anchor the centers of modern galaxies. And JWST is seeing smeared light from many early galaxies, indicating that their gas, too, is being slung around by a central supermassive black hole. How, then, did the big black holes get there?

Since black holes were first predicted as a consequence of Albert Einstein’s theory of gravity, astrophysicists have imagined how they might form from the inward gravitational collapse of dying stars. They now know that the cosmos is filled with black holes formed in this way. But cosmologists have struggled to understand supermassive black holes. These black holes somehow grew large enough, and fast enough, to shape the galaxies that formed around them. If they began as collapsed stars, they would have had to grow at staggering rates that defy physical explanation.

Some cosmologists have begun to favor an alternative theory for supermassive black hole seeds: that the black holes formed directly from the collapse of enormous clouds of gas in the young universe. This process could produce gargantuan black holes contemporaneous with galaxies like JADES-GS-z14-0.

Again, there are problems. Some of the early galaxies that seem to host supermassive black holes do not produce X-rays, which is typically a hallmark of black holes. Maybe those black holes produce X-rays that are too faint or too heavily obscured, so we don’t see them.

Some supermassive black holes do come with copious X-rays. In 2023, combined observations from JWST and the Chandra X-ray telescope unveiled a supermassive black hole in place just 470 million years after the Big Bang, in a galaxy labeled UHZ1. Could it have formed directly from the collapse of massive gas clouds, or from the implosion of a first-generation gargantuan star? “You either need modest growth of heavy initial seeds, versus accelerated growth of light seeds,” explained Priyamvada Natarajan of Yale University, who helped develop the “heavy seed” theory.

Modelers are still working out possibilities, but the early black hole in UHZ1 is a huge beacon, in terms of its energy across the electromagnetic spectrum, she said. That comment sparked pushback from Joseph Hennawi of the University of California, Santa Barbara, who questioned whether the object’s energy output really represents its mass.

“In my opinion, a lot of the claims and possibly some of the confusion is coming from the fact that we don’t have a handle on the bolometric power,” he said, referring to an object’s total power output. “I don’t think we need to believe the numbers that people are arguing.”

Natarajan countered that the measurements of the black hole’s energy density are the best we have so far, and that they come from two independent detection methods.

“It’s still very much open season, I think, for theorists, but evidence for heavy seeds is mounting,” she added.

Little Red Dots

JWST has unveiled a new class of cosmic objects. They are colloquially called little red dots — a familiar and friendly term for something in the early universe that we have never seen before or since.

The LRDs seem to be small, red-tinted galaxies that ignited about 600 million years after the Big Bang and blazed for a billion years. There is no trace of them in today’s universe. They are actually red, not just redshifted, which might suggest that they either emit ample red light or are full of dust that blocks blue wavelengths and leaves the object looking ruddy. The little red dots are tiny, some of them about 100 times smaller than today’s Milky Way. And this is pretty much all astronomers know about them, Pacucci said.

Andrey Kravtsov of the University of Chicago said that little red dots are the biggest discovery of JWST so far. As a theorist, he said, he had not heard much about them before the meeting. He said it reminded him of the discovery of quasars in the 1950s, mysterious ultra-luminous objects that turned out to be active supermassive black holes.

“This feels a lot like that — there are ideas flying around, and people can argue,” he said. “In a few years, it will be figured out. But right now it’s exciting to be in this process of discovery.”

As Kravtsov and I chatted, our table mates started talking about why little red dots are so unusual. The objects are spinning super fast, Dale Kocevski of Colby College told me — gas in the clouds is being flung around at 3,000 kilometers per hour. Typical gas flow is about 300 kilometers per hour. Only something huge can accelerate gas to those speeds, so some people argue the LRDs contain spinning supermassive black holes.

“But there are ways out of it,” countered Erica Nelson of the University of Colorado, Boulder. Her presentation described how, if LRDs are really tight, compact balls of gas, the gas might actually spin around that quickly. She and Kocevski continued explaining the theories and their weak points to me.

“So now you see the beautiful confusion,” Kravtsov said.

Cosmic Grapes

Certain discoveries seemed to stick with people, and it was almost as though you could see ideas forming as people incorporated their colleagues’ findings into their own talks. One such presentation came from Seiji Fujimoto of the University of Texas, Austin, who showed new work demonstrating that bright massive galaxies might contain more than meets the eyepiece. He and collaborators studied a bright galaxy that JWST had imaged as it appeared 930 million years after the Big Bang. Using gravitational lensing, he was able to discern that it is not just one object, but a grapelike cluster of at least 15 individual star-forming clumps.

Astronomers buzzed about Fujimoto’s findings for the next two days. Somerville wondered whether all high-redshift galaxies are made of dense clumps like those grapes, and why computer simulations of galaxy formation are not reproducing those structures. Dense clumps could produce stars efficiently and quickly, and would shine brightly, so gobs of cosmic grapes could explain a lot about how galaxies got off the ground, she noted. “We need to think about this harder,” she said, in another phrase that came to characterize the gathering.

Viraj Pandya of Columbia University showed that even small early galaxies have weird characteristics. They are oddly elongated, with stars aligned in such a way as to give the galaxies a cigar or pickle shape. Pandya described them as “galaxies going bananas.” This new class of galaxies in the early universe has no counterpart in the universe today.

Another way to put it is that everything was weird during the universe’s first billion years. Galaxy size, brightness, mass and shape from that period are all weird. Black holes are weird. The efficiency of star formation is weird; the correlation between brightness, astronomical power and an object’s mass — essential for theoretical models — are not as astrophysicists expected. The presence of little red dots and chains of elongated galaxies: weird. Aren’t people baffled by all this weirdness?

Kocevski smiled as I kept saying things like this. No one feels baffled, he said. Being unsure, and thinking about what comes next, is the point of an innovative observatory like JWST. “That’s science,” he said.

More to Come

The firehose is not even all the way open. JWST is streaming new data every day, and the intensely competitive fight for time on the telescope is determining which discoveries will happen first. But that’s saying nothing of the coming generation of ground-based telescopes and new orbital telescopes.

Several people looked forward to being able to combine JWST measurements with ones from the Nancy Grace Roman Space Telescope, which like JWST will observe infrared light from the early universe to tackle cosmological questions. Roman will beam down a terabyte of data per day. Euclid, a European telescope that launched last year, will determine galactic redshifts, enabling useful comparisons with JWST findings. And people were buzzing about the forthcoming Vera Rubin Observatory, set for first light in April or May 2025. The Rubin Observatory will photograph the entire heavens every three days and will totally transform short-timescale astronomy, showing how stars evolve day to day. It is an incredibly rich time to study the stars.

Earlier in the summer, I talked with Julian Muñoz at the University of Texas, Austin, who has proposed some new theories for bursty star formation that could explain the early massive galaxies. “There are more good questions than time,” Muñoz said.

Under the auspices of a research program dedicated to the cosmic dawn, Muñoz and several other astronomers spent much of the summer at KITP before and after I joined them at the four-day conference. Visiting scholars live in apartments provided by the institute and share dinners and evening walks to talk about their ideas. The Santa Ynez mountains to the northeast, the Pacific to the west, and the Mediterranean-like charm of Santa Barbara add to the communal experience. During one of the breaks, I made myself leave the darkened lecture room to take in the surroundings.

I walked toward Santa Barbara’s sun-bleached coast. Kravtsov, who also spent all summer here, had told me where to find a snowy plover habitat, a 20-minute walk along the beach. I walked down bluffs blanketed in invasive ice plant, a succulent ground cover that overtook the headlands when it was introduced in the 1950s. Yellow and pink flowers popped up randomly through the tangles. “Beautiful confusion,” Kravtsov had said. Thoughts of time started to overwhelm me.

Eighty-three years ago, during World War II, the U.S. Army Corps of Engineers built the nearby Santa Barbara airport using land dredged from Mescalitan Island, site of a Chumash Indian settlement. Indigenous peoples had lived there for at least 11,000 years.

Some 340 million years earlier, the lunar tide periodically stranded backboned fish on a beach just like this one. Over millennia, those fish began to walk on land.

About 4 billion years before that, a passing star or supernova material stirred the gaseous remains of a star some astronomers call Coatlicue, and the gas collapsed, igniting our sun.

Nearly 9 billion years earlier, light from the galaxy now called JADES-GS-z14-0 shone forth. Kevin Hainline was the first person to see it, when he downloaded a batch of JWST data in January of this year. He stood up from his chair in surprise.

Editor’s note: Priyamvada Natarajan is a member of Quanta Magazine’s advisory board. Rachel Somerville works at the Flatiron Institute, which, like Quanta, is funded by the Simons Foundation. Affiliation with the Simons Foundation has no influence on our coverage.