Pristine Massive Star Formation Caught at the Break of Cosmic Dawn

Abstract

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 AMORE6 at redshift $z=5.7253$, multiply imaged by a foreground galaxy cluster. JWST spectra consistently detect $\mathrm{H}\beta$ at both positions, but [OIII]${}_{\lambda \lambda 4960,5008}$ remains undetected. This places a firm upper limit on its oxygen abundance, $<$0.19% of solar metallicity at 3$\sigma$, establishing itself as the most pristine galaxy by far. AMORE6 exhibits exceptional properties that indicate the presence of pristine massive star formation. Finding such an example at a relatively late cosmic time is surprising, but it also validates the basic ideas behind the Big Bang model.

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