The finding, detailed by a research team led by Cheng and colleagues in 2026, emerged from spectroscopic analysis of distant galaxies observed by JWST. Their spectra showed unmistakable signatures of low-mass stars that earlier instruments could not detect — stars that collectively add enormous mass to galaxies astronomers had thought were relatively modest in size.
Hidden Stars and the Skyscraper Effect
The team’s findings hinge on a straightforward analogy. “If a galaxy were a city, the brightest stars would be the skyscrapers you can immediately see from far away,” the researchers explained. For decades, astronomers studying distant galaxies could only detect the brightest, most massive stars — the cosmic skyscrapers. Their light dominates the observable signal from billions of light-years away.
The vast populations of smaller, dimmer stars remained invisible. Their individual light was too faint to reach Earth-based instruments, and their collective glow was drowned out by the brilliant massive stars that burned hot and fast nearby. Astronomers knew these small stars existed in theory — they always form alongside their larger siblings — but they had no way to count them directly in distant galaxies.
The James Webb Space Telescope changed that equation. Its infrared instruments can pierce through cosmic dust and detect light from stars that earlier telescopes like Hubble could never resolve. When the team examined the spectra of nine ancient galaxies, they found unmistakable evidence that these systems contain far greater numbers of small stars than anyone had predicted from brightness measurements alone.
Why Small Stars Matter for Galaxy Mass
In astronomy, estimating the mass of a galaxy has always involved an inference problem. Telescopes measure light, not mass directly. Astronomers use something called the initial mass function — a statistical distribution that describes how many stars of various sizes form in a given stellar population. The function tells scientists that for every massive, brilliant star, there should be dozens or hundreds of smaller, dimmer ones.
The problem is that the initial mass function used for distant galaxies has typically been calibrated on nearby stellar populations, like those in the Milky Way’s star clusters. Astronomers assumed that the same ratio of large to small stars would hold in the early universe. The new JWST data suggests that assumption may be wrong.
If these ancient galaxies contain more small stars than the standard model predicts, then their total stellar masses could be significantly higher than calculated. A galaxy that appeared to weigh a billion solar masses might actually contain two or three times that amount, with the extra mass locked up in stars too dim to see without JWST’s infrared sensitivity.
That matters because galaxy mass is one of the fundamental quantities in cosmology. It determines how galaxies evolve, how they influence their surroundings through gravity, and how they fit into models of cosmic structure formation. Get the mass wrong, and every downstream calculation inherits the error.
The Nine Galaxies Under Examination
The research team, credited as Cheng et al. in the 2026 findings, focused on nine galaxies captured by JWST. These objects date to the early universe, when the first galaxies were forming out of primordial gas. Their light has traveled for billions of years to reach the telescope’s mirrors.
Each galaxy in the sample showed the same surprising pattern. The spectral signatures did not match models that assumed a standard distribution of stellar masses. Instead, they pointed to a population dominated by smaller stars — the kind that burn quietly for trillions of years and contribute mass without contributing much visible light. These are red dwarfs and similar low-mass stars, the most common type of star in the modern universe but notoriously difficult to detect at cosmological distances.
The consistency across all nine galaxies suggests that the hidden-star phenomenon is not an anomaly. It may be a general feature of early galaxy formation, meaning the entire population of ancient galaxies could be more massive than catalogued.
Implications for Early Universe Models
The discovery has ripple effects across cosmology. If the first galaxies were more massive than believed, then models of how quickly stars formed in the early universe may need revision. Greater mass means stronger gravity, more gas retention, and potentially faster chemical enrichment of the interstellar medium as successive generations of stars live and die.
It also affects estimates of how rapidly the universe transitioned from a dark, neutral gas-filled state to one filled with ionized, star-lit regions — a period known as reionization. More massive galaxies with more stars could have driven this process faster than current models suggest, potentially solving long-standing puzzles about why reionization appears to have happened so early in cosmic history.
The findings may also help explain another JWST puzzle: why some early galaxies appear surprisingly mature and well-developed despite forming only a few hundred million years after the Big Bang. If these galaxies were more massive than their light suggested, they had more raw material to build structure quickly, making their apparent maturity less paradoxical.
What Happens Next
Astronomers will need to expand the sample beyond nine galaxies to confirm whether the hidden-star pattern holds across the broader population of early galaxies. If it does, the initial mass function for the early universe will require recalibration, and mass estimates for thousands of known distant galaxies may need upward revision.
Future JWST observations will likely target larger samples across different cosmic epochs, testing whether the ratio of small to large stars changes over time or remains consistent from the earliest galaxies to the present day. The answer will shape how astronomers interpret every deep-field image the telescope captures.
The findings also underscore JWST’s transformative role in cosmology. Every deep-field observation has the potential to reveal populations of objects that were simply invisible to previous generations of instruments. As the telescope continues its mission, expect more discoveries that quietly rewrite the numbers underpinning our understanding of cosmic history — and the mass of the universe’s very first cities.
— Priya Nair, science desk, AXO News