Astronomers once hailed Earendel as the most distant star ever seen, a lone beacon shining just 900 million years after the Big Bang. But fresh observations with the James Webb Space Telescope (JWST) suggest a twist: Earendel may not be a single star at all, but a compact star cluster held together by gravity.
If that’s the case, the object in the Sunrise Arc galaxy sitting nearly 12.9 billion light-years away could be a rare glimpse of the early ancestors of today’s globular clusters, giant star swarms that orbit galaxies like our own Milky Way.
Who ran the study?
The new research was led by Massimo Pascale of the University of California, Berkeley with collaborators Liang Dai, Brenda Frye, and Aliza Beverage. Their findings were published in The Astrophysical Journal Letters on July 31, 2025, under the title “Is Earendel a Star Cluster? Metal-poor Globular Cluster Progenitors at z ∼ 6”.
The team drew on deep archival data from JWST, focusing on its NIRSpec instrument which can split faint ancient light into spectra. This allowed them to investigate Earendel’s age, chemistry, and structure in unprecedented detail.
What the researchers did
The group compared Earendel’s spectrum with that of another bright knot in the Sunrise Arc, known as 1b, which is widely accepted as a star cluster. By fitting different stellar population models essentially templates of what clusters of various ages and metal contents look like. They tested whether Earendel behaved more like a lone star, a binary system, or a compact cluster.
The models included three leading stellar libraries BC03, BPASS, and FSPS each capturing slightly different details of star formation. By matching Earendel’s spectral fingerprint against these, the team measured its likely age and chemical makeup.
What they discovered
Both Earendel and 1b turned out to have very similar spectra. Each matched the expectations of a metal-poor star cluster with an age of between 30 and 150 million years far older than the short lifetimes of massive single stars. Their stellar populations also contained fewer heavy elements than the Sun, consistent with the early cosmic era in which they formed.
The evidence points to Earendel being not one shining giant but rather the blended light of many stars packed into a dense, gravitationally bound system. Its properties line up with those of proto–globular clusters, thought to be the ancestors of the star clusters we see orbiting galaxies today.
Why is it important?
If Earendel is indeed a cluster, it changes how astronomers interpret the brightest points of light magnified by cosmic lenses. It suggests that what looks like a single star in the far reaches of the universe may often be something larger and more complex.
It also ties Earendel into a bigger story: the formation of globular clusters, which remain mysterious relics of the early universe. Observing them at such an early stage provides clues about how galaxies built up their stellar populations and how tightly bound swarms of stars survived for billions of years.
A rare cosmic magnifying glass
Earendel owes its visibility to gravitational lensing, where a massive foreground galaxy cluster bends space-time and magnifies the background Sunrise Arc galaxy. This alignment boosts Earendel’s brightness thousands of times over, making it just visible to JWST’s sensitive instruments. Without this cosmic trick, its light would be far too faint to detect.
But lensing can also cause confusion: depending on the exact magnification, the source could be small enough to be a star or big enough to be a cluster. That uncertainty is why Earendel’s true nature has sparked such debate.
What comes next
Not all astronomers are fully convinced. Brian Welch, who first identified Earendel with the Hubble Space Telescope, notes that at JWST’s resolution, the spectra of stars and clusters can look deceptively similar. To settle the matter, researchers may need to monitor Earendel for microlensing tiny brightness flickers caused by just one star dominating the light. If the glow stays steady, the case for a cluster strengthens.
For now, Earendel remains a cosmic enigma. But whether star or cluster, it has already reshaped what we thought was possible to glimpse from the dawn of galaxies and it continues to challenge our understanding of the universe’s first light.
Study: The Astrophysical Journal Letters– Is Earendel a Star Cluster?