An international team of astronomers has used the James Webb Space Telescope to characterize the most chemically primitive star-forming galaxy ever observed — an ultra-faint speck of light from 13 billion years ago whose oxygen content is just 1/240th that of the Sun.
The findings, published in Nature on May 13, detail how the team achieved a definitive characterization of the galaxy known as LAP1-B, located at a redshift of 6.625, placing it roughly 800 million years after the Big Bang during the epoch of reionization. The discovery provides what scientists describe as a direct ancestral link to the mysterious “fossil galaxies” found orbiting the Milky Way today.
An Organic Magnifying Glass
LAP1-B is so faint that it is invisible in standard camera images, even those taken by the JWST. To study it, the research team led by Associate Professor Kimihiko Nakajima of Kanazawa University relied on gravitational lensing — the bending of light by a massive foreground galaxy cluster called MACS J0416, which magnified LAP1-B’s light roughly 100 times. The team then pointed the JWST’s ear-Infrared Spectrograph at the galaxy for more than 30 hours, capturing faint emission lines from hydrogen and oxygen gas.N
“I was instantly thrilled by the extreme lack of oxygen revealed in the data,” Nakajima said in a statement released by the University of Tokyo’s Institute for Cosmic Ray Research. “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.”
Fingerprints Of The First Stars
Beyond its record-low oxygen abundance, LAP1-B displayed a high carbon-to-oxygen ratio that aligns with theoretical predictions for material dispersed by the explosions of the universe’s first-generation stars. The galaxy’s stellar mass is capped below 3,300 times that of the Sun, meaning dark matter overwhelmingly dominates its composition.
These properties make LAP1-B a near-perfect match for the ultra-faint dwarf galaxies found in the Milky Way’s neighborhood — ancient, dim collections of old stars long described as “fossils of the universe.”
“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,” said Professor Masami Ouchi of the National Astronomical Observatory of Japan and the University of Tokyo.
A Fresh Perspective On Cosmic Origins
The finding makes it possible to map the formation of the initial elements and the earliest structures in the cosmos. In an effort to find the first galaxies to form, the team intends to use the JWST to seek even more primitive objects. Nakajima stated, “We hope this discovery represents a historic step in understanding how the elements that make up our own bodies were first born and accumulated across the Universe.”