The extremely rapid assembly of the earliest galaxies during the first billion years of cosmic history is a major challenge for our understanding of galaxy formation physics (1; 2; 3; 4; 5). The advent of JWST has exacerbated this issue by confirming the existence of galaxies in significant numbers as early as the first few hundred million years (6; 7; 8). Perhaps even more surprisingly, in some galaxies, this initial highly efficient star formation rapidly shuts down, or quenches, giving rise to massive quiescent galaxies as little as 1.5 billion years after the Big Bang (9; 10), however, due to their faintness and red colour, it has proven extremely challenging to learn about these extreme quiescent galaxies, or to confirm whether any exist at earlier times. Here we report the spectroscopic confirmation of a massive quiescent galaxy, GS-9209, at redshift, z = 4.658, just 1.25 billion years after the Big Bang, using JWST NIRSpec. From these data we infer a stellar mass of M_∗ = 3.8 ± 0.2 × 10¹⁰ M⊙, which formed over a ≃ 200 Myr period before this galaxy quenched its star formation activity at \({\rm{z}}={6.5}_{-0.5}^{+0.2}\), when the Universe was ≃ 800 million years old. This galaxy is both a likely descendent of the highest-redshift submillimetre galaxies and quasars, and a likely progenitor for the dense, ancient cores of the most massive local galaxies.

在宇宙历史的前十亿年中，最早的星系以极快的速度聚集，这是我们理解星系形成物理学的一个重大挑战(1;2;3;4;5)。JWST 的出现加剧了这个问题，它证实了早在最初几亿年就存在大量星系的情况 (6; 7; 8)。也许更令人惊讶的是，在一些星系中，这种最初的高效恒星形成迅速停止或熄灭，在大爆炸后短短 15 亿年 (9; 10) 就产生了巨大的静止星系，然而，由于它们的微弱性和红色，事实证明，了解这些极端静止的星系或确认早期是否存在这些星系极具挑战性。在这里，我们报告了使用 JWST NIRSpec 对大爆炸后仅 12.5 亿年的一个巨大静止星系 GS-9209 进行的光谱确认，该星系处于红移，z = 4.658。根据这些数据，我们推断出恒星质量为 M _∗ = 3.8 ± 0.2 × 10 ¹⁰ M ⊙，它是在该星系在\({\rm{z}}={6.5 处熄灭其恒星形成活动之前的≃ 200 Myr 周期内形成的}_{-0.5}^{+0.2}\)，当时宇宙的年龄≃ 8亿年。这个星系既可能是红移最高的亚毫米星系和类星体的后代，也可能是最大质量的本地星系的致密、古老的核心的祖先。