Population III (PopIII) stars represent astronomy’s ultimate prize: the first generation of stars born from the pristine hydrogen and helium created in the Big Bang. These theoretical giants, potentially hundreds of times more massive than our sun, should have been fundamentally different from any stars we see today. They contained virtually no “metals,” astronomy’s term for elements heavier than helium, because none existed yet in the universe.

Despite the incredible power of the James Webb Space Telescope (JWST), these ancient stars have remained frustratingly elusive. Traditional searches have focused on finding completely metal-free systems, looking for the brief signature of prominent helium emission without any heavy element contamination. This approach creates an impossibly narrow detection window.

The hunt has taken on an unexpected twist with new research led by Elka Rusta from Università degli Studi di Firenze in Italy that proposes a revolutionary approach: instead of seeking perfect purity, target galaxies during their “self-polluted” phase. This occurs when the first massive stars have exploded as supernovae and scattered heavy elements into the surrounding gas, but the original metal-free stars are still burning bright.

During this transitional period, PopIII galaxies can emit detectable metal lines while still hosting only metal-free stars. The gas shows chemical enrichment from the first supernovae, creating observable signatures even though the stars themselves formed from pristine material. This represents a much longer and more detectable window than the fleeting moment of complete metal absence.

The research, posted to the arXiv preprint server, reveals encouraging news about detection timeframes too. The distinctive helium emission from PopIII galaxies can last up to 20 million years, the team suggest, and remains partly visible even during the “hybrid” phase, when both first-generation and second-generation stars coexist. While brief in cosmic terms, this is dramatically longer than previously thought possible.

The team has developed new diagnostic tools using ultraviolet metal lines to identify candidates. When applied to existing JWST data from the JADES survey (JWST Advanced Deep Extragalactic Survey), they identified nine candidate galaxies with more than 25% of their stellar mass in metal-free stars, a significant increase over previous searches.

The new method looks for specific emission line ratios, particularly between doubly ionized oxygen and hydrogen beta, which opens the pool of candidates to more easily detectable sources. Rather than relying on the absence of signals, which is always challenging to confirm, this approach provides positive detections of characteristic patterns.

Successfully identifying metal-polluted PopIII galaxies would transform our understanding of the earliest period of the universe. These observations could reveal how the first heavy elements spread through early galaxies and trace the universe’s transformation from simplistic hydrogen/helium rich to the far more complex chemical cocktail we see today.