JWST Finds Early Galaxies Already Spreading Heavy Elements

A University of Arizona study found galaxies were producing and expelling carbon, oxygen and silicon just 500 million years after the Big Bang.

A University of Arizona team, publishing in Nature Astronomy, used the James Webb Space Telescope to study three distant galaxies whose light has traveled more than 13 billion years. First author Yongda Zhu said heavy elements escaped from galaxies very, very early in cosmic time, and that the galaxies were not only producing these elements but dispersing them, possibly seeding other galaxies.

Astronomers had long predicted that gas surrounding the very first galaxies would remain largely pristine, made mostly of primordial hydrogen and helium for an extended period. The new observations break that picture: only about 500 million years after the Big Bang — roughly 3% of the universe's current age — young galaxies had already forged heavier elements in their stars and begun redistributing them. The Brighter Side of News reports that the three infant galaxies already contained disturbed, multiphase, metal-rich gas, showing that cosmic chemical recycling began remarkably early.

According to University of Arizona News, Zhu manually searched publicly available JWST spectra from hundreds of galaxies over one long night and pinpointed three with absorption patterns indicating heavy elements. The galaxies, at redshifts between about 7.3 and 9.3, were used as their own background light sources: as their starlight passed through surrounding gas, atoms absorbed specific wavelengths, leaving chemical fingerprints. The Brighter Side of News reports the data came from the SPURS survey with JWST's NIRSpec instrument, requiring deep exposures approaching 30 hours — measurements that were nearly impossible before JWST.

The discovery shows that baryon cycling — the exchange of material between galaxies and their surroundings — was already operating during the Epoch of Reionization. It may also explain why astronomers have struggled to find Population III stars, the hypothetical first stars formed from pristine gas. Zhu compared the enrichment to sprinkles mixed into vanilla ice cream: once mixing begins early, truly pristine gas may not have survived long enough to observe.