近日，日本金泽大学Kimihiko Nakajima团队报道了在再电离时代形成的一种超微弱的化学原始星系。该项研究成果发表在2026年5月13日出版的《自然》杂志上。

第一代恒星与星系的形成标志着化学增丰的开端，但对此类原始系统的直接观测至今仍遥不可及。

研究组展示了詹姆斯·韦伯太空望远镜对LAP1-B的光谱观测结果。LAP1-B是一个红移z_spec = 6.625 ± 0.001的超微弱星系，对应宇宙大爆炸后8亿年的宇宙年龄。该星系受到强引力透镜的显著放大。LAP1-B的气相氧丰度为太阳值的(4.2 ± 1.8) × 10^-3倍，使其成为迄今发现化学上最原始的恒星形成星系。该星系展现出异常硬的电离辐射场，这与化学增丰的恒星种群或吸积黑洞不一致，但符合极端贫金属恒星种群的理论预测。

同时，在其星际介质中，对于其金属丰度而言，该星系显示出较高的碳氧丰度比，这与无初始金属条件下形成的恒星种群的核合成产额一致。由于探测不到恒星连续谱，其恒星质量被限制在3300倍太阳质量以下；而由发射谱线运动学推算的动力学质量超过了恒星质量与气体质量之和，表明存在占主导地位的暗物质晕。该发现确立了LAP1-B作为“正在形成的化石”——即本地宇宙中观测到的古老超微弱矮星系的直接高红移前身，并为星系形成的最早阶段提供了一个稀有的观测窗口。

附：英文原文

Title: An ultra-faint, chemically primitive galaxy forming in the reionization era

Author: Nakajima, Kimihiko, Ouchi, Masami, Harikane, Yuichi, Vanzella, Eros, Ono, Yoshiaki, Isobe, Yuki, Nishigaki, Moka, Tsujimoto, Takuji, Nakamura, Fumitaka, Xu, Yi, Umeda, Hiroya, Zhang, Yechi

Issue&Volume: 2026-05-13

Abstract: The formation of the first stars and galaxies marked the onset of chemical enrichment, yet direct observations of such primordial systems remain elusive. Here we present James Webb Space Telescope spectroscopic observations of LAP1-B, an ultra-faint galaxy at redshift zspec = 6.625 ± 0.001, corresponding to a cosmic age of 800 million years after the Big Bang. This galaxy is strongly magnified by gravitational lensing. LAP1-B exhibits a gas-phase oxygen abundance of (4.2 ± 1.8) × 103 times the solar value, making it the most chemically primitive star-forming galaxy discovered to date. The galaxy displays an exceptionally hard ionizing radiation field, which is inconsistent with chemically enriched stellar populations or accreting black holes but matches theoretical predictions for an exceptionally metal-deficient stellar population1. It also shows an elevated carbon-to-oxygen abundance ratio for its metallicity in the interstellar medium, consistent with nucleosynthetic yields from a stellar population formed in the absence of initial metals2,3,4. The lack of detectable stellar continuum constrains the stellar mass to below 3,300M⊙, and the dynamical mass, derived from emission-line kinematics, exceeds the combined stellar and gas mass, which indicates a dominant dark matter halo. Our findings establish LAP1-B as a ‘fossil in the making’, a direct high-redshift progenitor of the ancient ultra-faint dwarf galaxies observed in the local Universe and offers a rare window into the earliest stages of galaxy formation.

DOI: 10.1038/s41586-026-10374-1

Source: https://www.nature.com/articles/s41586-026-10374-1