Young galaxies should be vigorously forming stars, yet Webb found them pausing.
In the universe's first billion years, when galaxies were expected to burn brightest with the fury of new star creation, fourteen of them had already gone quiet. An international team led by doctoral student Alba Covelo Paz, using the James Webb Space Telescope's unprecedented infrared vision, found these dormant galaxies spanning a wide range of masses — a discovery that suggests the rhythm of cosmic birth and pause is not a late development in the universe's story, but one written into its earliest chapters. The finding invites us to reconsider what we thought we knew about the tempo of creation itself.
- Astronomers expected the infant universe to be a relentless forge of new stars — instead, Webb found fourteen galaxies that had already fallen silent within the cosmos's first billion years.
- Stellar feedback — the shockwaves of supernovas and the force of stellar winds — appears to have expelled the cold gas these galaxies needed to keep building, triggering pauses of ten to twenty-five million years.
- The discovery's breadth is what unsettles old models most: previous dormant finds clustered at mass extremes, but this new sample fills the middle ground, suggesting cosmic quiet is common, not a rare anomaly.
- The critical question — whether these galaxies will reawaken or remain permanently dark — cannot yet be answered, and the difference between a pause and a death may rewrite theories of galaxy evolution.
- A dedicated Webb program called 'Sleeping Beauties' is now being designed to track these galaxies over time, hunting for the moment of reignition or confirming a silence that never ends.
The James Webb Space Telescope has found something the early universe was not supposed to contain: galaxies that had already stopped making stars. Led by doctoral student Alba Covelo Paz at the University of Geneva, an international team identified fourteen dormant galaxies within the cosmos's first billion years — a finding that challenges the long-held assumption that young galaxies should be in a constant, furious state of stellar assembly.
Webb's infrared spectroscopy, far more sensitive than anything Hubble could offer, revealed these fourteen galaxies across a striking range of masses — from roughly forty million to thirty billion times the mass of our sun — all sharing the same quiet signature: middle-aged and older stars, but no new ones being born. The likely culprit is stellar feedback, the violent outward force of supernovas and stellar winds that heats and expels the cold gas galaxies need to keep forming stars. Each of the fourteen appeared to have been dormant for between ten and twenty-five million years, suggesting a temporary lull rather than a permanent end.
What gives the discovery its weight is its breadth. Before Webb, only four dormant early-universe galaxies had ever been found, and they sat at the extremes of the mass spectrum. This new sample fills the middle ground, implying that stop-and-go star formation may be a universal feature of how galaxies grow, not a rare outlier behavior.
Still, the deeper question remains open. Paz's team cannot yet confirm whether these galaxies will eventually reignite or stay silent indefinitely — a dormancy lasting fifty million years or more would point to a different, more permanent mechanism at work. An upcoming Webb observing program called 'Sleeping Beauties' aims to find more such galaxies and watch them over time, hoping to catch the moment of reawakening — or to confirm that some cosmic fires, once extinguished, do not return.
The James Webb Space Telescope has revealed something astronomers did not expect to find in the infant universe: galaxies that have stopped making stars. An international team of researchers, led by doctoral student Alba Covelo Paz at the University of Geneva, discovered fourteen of these dormant galaxies within the first billion years after the Big Bang—a finding that upends assumptions about how the earliest galaxies should behave.
When galaxies are young, the thinking went, they should be furiously assembling new stars. Yet Webb's sensitive spectroscopic data, which can detect light shifted into the infrared and analyze its composition in ways the older Hubble telescope could not, revealed something different. These fourteen galaxies, ranging in mass from about forty million to thirty billion times the sun's weight, had all paused their star formation. The discovery matters because it suggests that the stop-and-start rhythm of galaxy building is not a late-universe phenomenon but something that happened when the cosmos was still in its first billion years.
The mechanism behind these pauses appears to be stellar feedback—the violent processes that accompany massive star birth. When supernovas detonate or stellar winds blow outward with tremendous force, they heat and expel the cold gas that galaxies need to keep making stars. This gas, once driven away, takes time to cool and fall back. Paz's team found that all fourteen dormant galaxies had been quiet for between ten and twenty-five million years, suggesting they were caught in a temporary lull rather than permanently dead. The presence of middle-aged and older stars in their light, combined with an absence of new ones, told this story.
What makes this discovery significant is its breadth. Before Webb, astronomers had identified only four dormant galaxies in the early universe, and they clustered at the extremes—either very light or very heavy. The new sample spans the middle ground, showing that dormancy is not confined to unusual outliers but appears across a range of galaxy masses. This suggests the stop-and-go pattern of star formation may be a common feature of how galaxies grow, not a rare exception.
Yet uncertainty remains. Paz emphasized that the team cannot yet confirm whether these galaxies will resume star formation or remain asleep indefinitely. If they stay dormant for fifty million years or longer, it would indicate a different mechanism at work—one that truly kills the galaxy rather than merely pausing it. The current evidence points toward temporary quiescence, but only future observations will settle the question.
An upcoming Webb program called "Sleeping Beauties" will be dedicated to finding and studying more of these dormant galaxies. By observing them over time, astronomers hope to measure how long the quiet phase lasts and whether the galaxies eventually reignite their star-making engines. Each observation brings the field closer to understanding the rhythm of galaxy evolution—the pattern of bursts and silences that shaped the universe we see today.
Notable Quotes
The first discovery of a dormant galaxy in the early universe was such a shock because that galaxy had been observed before with Hubble, but we could not know it was dormant until JWST.— Alba Covelo Paz, lead researcher
We now found 14 sources supporting this burstiness process, and we found that all of them have halted star formation between 10 and 25 million years before we observed them.— Alba Covelo Paz
The Hearth Conversation Another angle on the story
Why would astronomers be surprised to find dormant galaxies so early in the universe's history?
Because galaxies that young should be in their most vigorous phase. They have fresh material, gravity is pulling everything together, and there's no reason they should be taking a break. It's like finding a newborn sleeping through dinner.
What actually stops them from making stars?
Mostly violence, paradoxically. Supernovas and stellar winds heat up the cold gas galaxies need as fuel. The gas gets blown away or warmed so much it can't collapse into new stars. It's a self-limiting process—the very act of making stars can shut down star-making.
So they're not dead, just resting?
That's the working hypothesis. These fourteen galaxies have been quiet for ten to twenty-five million years, which is short enough that the gas could still come back and cool down. But we can't be certain. If they stay dormant much longer, it means something else killed them permanently.
How did Webb see something Hubble couldn't?
Hubble can see these distant galaxies, but it can't analyze their light in detail. Webb's spectroscopic instruments can break down the infrared light these galaxies emit and read the fingerprints of old stars versus new ones. That's how we know they've stopped forming.
What changes if this turns out to be common?
Everything about how we think galaxies grow. If dormancy is a normal part of the process, then galaxy evolution isn't a smooth climb but a stutter-step. You'd have to rethink the whole timeline of how the universe built itself.
What happens next?
Webb will keep looking for more of these sleeping galaxies. The real test is whether we catch any of them waking up, or whether they stay asleep. That will tell us if this is a temporary pause or a permanent shutdown.