The Cosmic Gems arc is among the brightest and highly magnified galaxies observed at redshift z ∼ 10.2¹. 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 ∼ 10⁶ M_⊙. Their lensing-corrected sizes are approximately 1 pc, resulting in stellar surface densities near 10⁵ M_⊙ /pc², three orders of magnitude higher than typical young star clusters in the local universe⁷. 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.

宇宙宝石弧是在红移 z ∼ 10.2 ¹ 处观察到的最亮和高度放大的星系之一。然而，它本质上是一个紫外线微弱星系，处于现在被认为驱动宇宙再电离的范围内 ^2–4 。迄今为止，在可比较的红移下，星系中解析的最小特征在几百到几十秒差距之间 ^5,6 。在这里，我们报告了 JWST 对宇宙宝石的观测结果。星系的光被分解成位于小于 70 秒差距的区域中的五个星团。它们表现出最小的粉尘衰减和低金属丰度，年龄小于 50 Myr，内在质量为 ∼ 10 ⁶ M _⊙ 。它们的透镜校正尺寸约为 1 pc，导致恒星表面密度接近 10 ⁵ M _⊙ /pc ² ，比典型的年轻恒星高三个数量级本地宇宙中的星团 ⁷ 。尽管透镜模型存在固有的不确定性，但它们与引力束缚的恒星系统（即原球状星团（proto-GC））一致。我们得出的结论是，在再电离时期，星团的形成和反馈可能有助于塑造星系的特性。