The element abundance ratios of four low-mass stars with extremely low metallicities (abundances of elements heavier than helium) indicate that the gas out of which the stars formed was enriched in each case by at most a few—and potentially only one—low-energy supernova. Such supernovae yield large quantities of light elements such as carbon but very little iron. The dominance of low-energy supernovae seems surprising, because it had been expected that the first stars were extremely massive, and that they disintegrated in pair-instability explosions that would rapidly enrich galaxies in iron5. What has remained unclear is the yield of iron from the first supernovae, because hitherto no star has been unambiguously interpreted as encapsulating the yield of a single supernova. Here we report the optical spectrum of SMSS J031300.36−670839.3, which shows no evidence of iron (with an upper limit of 10−7.1 times solar abundance). Based on a comparison of its abundance pattern with those of models, we conclude that the star was seeded with material from a single supernova with an original mass about 60 times that of the Sun (and that the supernova left behind a black hole). Taken together with the four previously mentioned low-metallicity stars, we conclude that low-energy supernovae were common in the early Universe, and that such supernovae yielded light-element enrichment with insignificant iron. Reduced stellar feedback both chemically and mechanically from low-energy supernovae would have enabled first-generation stars to form over an extended period. We speculate that such stars may perhaps have had an important role in the epoch of cosmic reionization and the chemical evolution of early galaxies.
这项研究描述了在持续进行中的SkyMapper Southern Sky Survey中所发现的一个引人注目的恒星。被称为SMSS 0313–6708的这个恒星的光谱显示它没有可以检测得到的铁，这说明它的铁含量至少要比以前所知含铁量最低恒星低30倍。作者的结论是，这个恒星的化学组成带有原始质量约为太阳质量60倍的一颗超新星的爆炸印记。与四个以前发现的低金属恒星（这里所说的“金属”是指任何一种比氦重的元素）所做比较表明，低能超新星在早期宇宙中也许是普遍的，这种超新星产生了铁含量不高的轻元素富集。这些低铁恒星也许能让我们有机会一瞥宇宙再电离和早期星系的化学演变等过程。