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 H$β$ at both positions, but [OIII]$λλ$4960,5008 remains undetected. This places a firm upper limit on its oxygen abundance, < 0.12 % of solar metallicity at 2$σ$, 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.