Thirteen billion years ago, when the universe was still in its infancy, a tiny galaxy called LAP1-B was already doing something remarkable: it was patiently waiting to tell us its story. That story has now been heard, thanks to the James Webb Space Telescope and a cosmic accident that turned a massive galaxy cluster into a natural magnifying glass.
An international team led by Kimihiko Nakajima of Kanazawa University has captured the chemical fingerprint of LAP1-B, an ultra-faint galaxy from just a few hundred million years after the Big Bang. The finding, published in Nature, marks the first time astronomers have definitively characterized a galaxy from such an early epoch—and what they found has rewritten their understanding of how the first stars shaped the cosmos.
When the universe began, it contained only hydrogen and helium. All the heavier elements—oxygen, carbon, iron—were forged later, inside the cores of the very first stars, then scattered across space when those stars died. For decades, scientists have searched for the moment these primordial stars began enriching the cosmos with heavier elements. The problem: the earliest galaxies were impossibly small and faint, their chemical signatures lost in the noise of distant, dazzling lights.
Gravitational lensing changed that. The researchers used a massive galaxy cluster as a natural telescope, which magnified LAP1-B's light 100 times over. Staring at the same patch of sky for more than 30 hours with JWST's Near-Infrared Spectrograph, they measured an oxygen abundance that made Nakajima's breath catch: just 1/240th of what our sun contains today.
"I was instantly thrilled by the extreme lack of oxygen," Nakajima said. "Finding a galaxy in such a primitive state is astonishing. It's a chemical signature that clearly indicates a primordial galaxy caught in the moments shortly after its formation."
The galaxy also revealed a high carbon-to-oxygen ratio, matching theoretical predictions for material scattered by the universe's first generation of supernovae. At less than 3,300 times the mass of our sun, LAP1-B is extraordinarily lightweight—meaning most of it is made of invisible dark matter. This chemical fingerprint and its puny mass make it a near-perfect match for the ultra-faint dwarf galaxies (UFDs) found orbiting near our Milky Way today, dim collections of ancient stars that have remained largely unchanged for over 12 billion years.
"UFDs are not only the faintest galaxies; they are composed of ancient stars over 12 billion years old and are often described as 'fossils of the universe,'" said co-author Masami Ouchi of the National Astronomical Observatory of Japan and the University of Tokyo. "Astronomers suspected they might be the remains of the universe's earliest galaxies because they lack heavy elements, but astronomers never had a direct link—until we found LAP1-B."
Ouchi called it a profound surprise to find LAP1-B looks exactly like the "ancestor" scientists had only imagined in theories. The discovery establishes a new way to map the birth of elements and the formation of the universe's oldest structures. The team now plans to search for even more primitive objects, seeking the very first galaxies that ever formed—and perhaps finally understanding why these cosmic fossils have survived, unchanged, to the present day.