A study in Nature reports that JWST observations of the tiny galaxy LAP1-B have revealed the most chemically primitive star-forming galaxy discovered so far. Seen as it existed about 800 million years after the Big Bang, the galaxy carries an unusually faint chemical imprint from the early universe.
The international team, led by Kimihiko Nakajima of Kanazawa University, used the James Webb Space Telescope and the magnifying power of a foreground galaxy cluster to study an object far too faint for ordinary observations. The result is a rare look at a galaxy near the dawn of cosmic chemical history.
Its most striking feature is its oxygen content. The researchers found that LAP1-B has only about 1/240 of the Sun’s oxygen abundance. That makes it an extraordinary target for astronomers trying to learn how the first stars changed the universe from a simple mix of hydrogen and helium into a cosmos rich with carbon, oxygen and heavier elements.
A galaxy from 800 million years after the Big Bang
About 13 billion years ago, the universe was still young. The first generations of stars had begun to shine, explode and seed space with heavier elements. LAP1-B appears in that ancient period, during the reionization era, when early galaxies were helping transform the foggy young universe into a more transparent one.
The Nature study places LAP1-B at a spectroscopic redshift of 6.625. In practical terms, Webb is seeing light that began its journey when the universe was roughly 800 million years old. That makes the galaxy a time capsule from a period when many of the familiar ingredients of later galaxies were still scarce.
For astronomers, the galaxy’s faintness is part of its value. Bright early galaxies are easier to find, but they often represent the more massive and active side of early cosmic evolution. LAP1-B gives researchers access to a smaller system, closer to the scale of the tiny building blocks that may have helped assemble larger galaxies over time.
The observations focused on the galaxy’s light spectrum. A spectrum breaks light into signatures from different atoms and ions. Those signatures let astronomers estimate the chemical mixture of the gas, the intensity of radiation from young stars and the physical conditions inside a galaxy that can’t be visited or resolved in everyday detail.
The lowest oxygen level yet measured
The headline result is the galaxy’s record-low oxygen abundance. In astronomy, oxygen is a crucial marker because it is made inside stars and released into space by stellar death. A galaxy with extremely little oxygen has undergone very limited chemical enrichment.
The team measured a gas-phase oxygen abundance of about 0.0042 times the solar value. That is roughly 1/240 of the Sun’s oxygen abundance. The Nature abstract describes LAP1-B as the “most chemically primitive star-forming galaxy discovered to date.”
This does mean the galaxy is empty of stars. The study identifies it as a star-forming galaxy, which means young stars are present or recently formed. Its primitive chemistry shows that only a small amount of previous stellar processing had occurred before Webb observed it.
Oxygen is especially useful because it leaves measurable fingerprints in galaxy spectra. When hot young stars energize surrounding gas, atoms emit light at specific wavelengths. Webb’s infrared instruments can detect those signals after cosmic expansion stretches the light during its long trip across space.
The low oxygen content also points to a short chemical history. Stars need time to manufacture heavier elements and disperse them. LAP1-B appears to have been caught near the beginning of that process, when the local supply of heavier elements remained extremely small.
A natural lens made the galaxy visible
LAP1-B is so faint that Webb needed help from the universe itself. The study relied on gravitational lensing, a natural effect caused by the gravity of a massive foreground galaxy cluster. The cluster bends and amplifies light from more distant objects behind it.
In this case, lensing made the distant galaxy bright enough for detailed study. The background information from the research team describes LAP1-B’s light as amplified by roughly 100 times. That boost allowed JWST to collect spectral data from an object that would otherwise sit beyond the reach of detailed chemical analysis.
Webb’s contribution came from its sensitivity to infrared light. As light travels from very distant galaxies, the expansion of the universe stretches it into longer wavelengths. The JWST NIRSpec instrument can split that faint infrared light into a spectrum, giving astronomers a chemical readout from the early universe.
The research team observed the target for more than 30 hours. Long exposures matter for galaxies this faint because every additional hour adds more photons to the signal. The final data gave the team enough information to estimate the galaxy’s chemical state and compare it with models of early stellar populations.
Together, Webb and the lensing cluster acted like a two-part observatory. One part collected faint infrared light in space. The other part came from gravity on a cosmic scale, which magnified a small galaxy from deep time.
Clues from the universe’s first stars
The study also found an elevated carbon-to-oxygen ratio for a galaxy with such low metallicity. That chemical pattern matters because the first stars are expected to have created and released elements in ways that differ from later generations of stars.
After the Big Bang, the universe consisted mainly of hydrogen and helium. Carbon, oxygen and other heavier elements were forged later inside stars. When massive stars died, they scattered those elements into surrounding gas. New stars and galaxies then formed from material that carried the chemical record of earlier generations.
The Nature paper reports that LAP1-B’s chemical signature is consistent with theoretical yields from stars formed in the absence of initial metals. Astronomers often refer to those hypothetical first stars as Population III stars. Their direct detection remains one of the major goals of early-universe astronomy.
LAP1-B gives researchers a nearby clue in cosmic time. The galaxy’s very low oxygen content and unusual carbon signal suggest that only a small number of earlier stellar events may have enriched its gas. That makes it a promising laboratory for studying how the first heavy elements entered young galaxies.
The team also found an exceptionally hard ionizing radiation field. In plain terms, the galaxy’s young stellar population appears to be producing very energetic light. The study reports that this radiation pattern matches expectations for an extremely metal-poor stellar population.
A possible ancestor of Milky Way fossils
LAP1-B may also help connect the early universe with nearby galactic fossils. The study reports that the galaxy’s stellar mass is below 3,300 solar masses. That is extraordinarily small for a galaxy, even by dwarf-galaxy standards.
The researchers also found evidence that the system is dominated by a dark matter halo. Dark matter cannot be seen directly, but its gravity shapes how gas and stars move. In tiny galaxies, that invisible scaffolding can make up most of the total mass.
Those traits resemble ultra-faint dwarf galaxies near the Milky Way. These nearby systems contain very few stars, have low chemical abundances and preserve stellar populations older than 12 billion years. Astronomers have long treated them as relics from early cosmic history.
The Nature abstract calls LAP1-B a “fossil in the making.” That phrase captures why the discovery is so useful. Webb is observing a tiny, chemically primitive galaxy in the early universe, while astronomers can also study ancient ultra-faint dwarfs around the Milky Way today.
If that link holds, LAP1-B could show what some of those nearby fossil galaxies looked like when they were young. It gives researchers a bridge between two kinds of evidence, the distant light of early galaxies and the old stars preserved in the Milky Way’s neighborhood.
The finding also shows how Webb can probe smaller and fainter targets than previous observatories could study in detail. With more lensed galaxies and deeper spectra, astronomers may build a clearer map of how the first stars enriched the smallest galaxies. LAP1-B is one of the sharpest glimpses yet of that beginning.
