Pristine Massive Star Formation Caught at the Break of Cosmic Dawn

The existence of galaxies with no heavy elements is a key prediction of cosmological models. So far no "zero-metallicity", or Population III, galaxies have been identified. Here, we report the identification of an extremely metal-poor galaxy at redshift z = 5. 725 ("AMORE6"), multiply imaged by a foreground galaxy cluster. JWST spectra consistently detect Hβ at both positions, but OIIIλλ4960, 5008 remains undetected. This places a firm upper limit on its oxygen abundance, < 0. 12 % of solar metallicity at 2σ, establishing itself as the most pristine object by far. AMORE6 exhibits exceptional properties that indicate the presence of pristine massive star formation. The finding of such an example at a relatively late cosmic time is surprising, but it also validates the basic ideas behind the Big Bang model.