Bound star clusters observed in a lensed galaxy 460 Myr after the Big Bang.

The Cosmic Gems arc is among the brightest and highly magnified galaxies observed at redshift z ∼ 10.2 1 . However, it is an intrinsically UV faint galaxy, in the range of those now thought to drive the reionization of the universe 2-4 . Hitherto the smallest features resolved in a galaxy at a comparable redshift are between a few hundreds and a few tens of parsecs 5,6 . Here we report JWST observations of the Cosmic Gems. The light of the galaxy is resolved into five star clusters located in a region smaller than 70 parsec. They exhibit minimal dust attenuation and low metallicity, ages younger than 50 Myr and intrinsic masses of ∼ 10 6 M ⊙ . Their lensing-corrected sizes are approximately 1 pc, resulting in stellar surface densities near 10 5 M ⊙ /pc 2 , three orders of magnitude higher than typical young star clusters in the local universe 7 . Despite the uncertainties inherent to the lensing model, they are consistent with being gravitationally bound stellar systems, i.e., proto-globular clusters (proto-GCs). We conclude that star cluster formation and feedback likely contributed to 3 shape the properties of galaxies during the epoch of reionization.