Astronomers using the James Webb Space Telescope have identified what may be the most distant barred spiral galaxy ever discovered, dating to a time less than 1.2 billion years after the Big Bang. The paper outlining its properties was posted to the arXiv preprint server on June 23.
Galactic funnels
Stellar bars are elongated formations of stars that stretch across a galaxy’s central region, spinning together as a single, unified structure. Through this rotation, they function much like a funnel, channeling gas toward the galactic center. This can ignite bursts of star formation, supply material to the central black hole and contribute to the buildup of a compact core. Such structures are common among galaxies in the local universe, and our own Milky Way is one example of a barred galaxy.
But bars don’t just form anywhere. They take shape in galaxies where stars move in smooth and orderly fashion, with something called a dynamically “cold” disk. Early-universe galaxies were the opposite: turbulent and gas-rich, constantly disrupted by mergers and bursts of star formation, conditions that should keep disks “hot” and unsettled for billions of years.
Observations supported this notion until recently, when the James Webb Space Telescope (JWST) started identifying bars in early galaxies. The emergence of more and more barred galaxies suggests that some galaxies were able to settle into orderly, rotating disks much faster than previously thought.
In the present study, astronomers report the discovery of M1149-BSG-z5, a barred spiral galaxy candidate at z = 5.102. The team, led by Xiaohan Wang of Tsinghua University, used JWST and the Hubble Space Telescope to understand what’s special about it.
Too young, so mature!
Using a technique called isophotal analysis, which tracks how the shape and orientation of the galaxy’s brightness contours change while moving outward from the center, the researchers studied the galaxy’s underlying structure. It revealed a bar, which was also confirmed by modeling its overall structure.
The galaxy also appeared to have spiral arms. “The discovery of M1149-BSG-z5 and its structural and global properties suggests that bars emerge as early as z > 5,” the team writes in the paper.
The galaxy itself is massive, with a stellar mass of about 28 billion solar masses. It is forming stars at a rate of roughly 145 solar masses per year. With an effective radius of roughly 8,500 light-years, M1149-BSG-z5 is “larger than typical galaxies at z ∼ 5, but comparable to barred galaxy sizes at 2
Finally, the researchers looked at the galaxy’s chemical makeup by analyzing the ratios of different emission lines in its spectrum. What they found supports the idea that M1149-BSG-z5 is chemically mature. “… the emission-line ratios are difficult to reconcile with a very metal-poor interpretation, and instead suggest that the gas is already chemically enriched in M1149-BSG-z5,” the team explains.
The researchers also found some signs of an actively feeding supermassive black hole at the center. Notably, this black hole is smaller relative to the galaxy’s stellar mass than is typical for black holes in other early-universe galaxies. Instead, it resembles ratios seen in present-day galaxies.
Fueling chaos
The galaxy, therefore, already shows a well-developed stellar bar and spiral arms and is chemically evolved, with a central bulge and an actively growing supermassive black hole—features that are typically associated with much more mature galaxies.
The researchers also found evidence that the galaxy resides in a crowded environment, with a nearby companion located some 70,000 light-years away, hinting at the possibility of a past gravitational interaction.
They are not yet sure whether the bar formed spontaneously within an already calm, orderly disk or whether it was set off by an external push, such as a merger or close interaction with this other galaxy.
“Further follow-up observations, particularly kinematic measurements of M1149-BSG-z5, would be the key to confirm its baryon dominance and help to determine the bar formation mechanisms in the early universe,” the team concludes.
To confirm the bar’s presence with confidence, researchers require follow-up observations to measure how the stars and gas are actually moving along the structure.
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Publication details
Xiaohan Wang et al, A massive barred spiral galaxy at z = 5.102 discovered by JWST, arXiv (2026). DOI: 10.48550/arxiv.2606.25022
Journal information:
arXiv
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JWST finds the most distant barred galaxy candidate in the early universe (2026, July 7)
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