In the transitional mass range (~8–10 solar masses) between white dwarf formation and iron core-collapse supernovae, stars are expected to produce an electron-capture supernova. Theoretically, these progenitors are thought to be super-asymptotic giant branch stars with a degenerate O + Ne + Mg core, and electron capture onto Ne and Mg nuclei should initiate core collapse^1,2,3,4. However, no supernovae have unequivocally been identified from an electron-capture origin, partly because of uncertainty in theoretical predictions. Here we present six indicators of electron-capture supernovae and show that supernova 2018zd is the only known supernova with strong evidence for or consistent with all six: progenitor identification, circumstellar material, chemical composition^5,6,7, explosion energy, light curve and nucleosynthesis^8,9,10,11,12. For supernova 2018zd, we infer a super-asymptotic giant branch progenitor based on the faint candidate in the pre-explosion images and the chemically enriched circumstellar material revealed by the early ultraviolet colours and flash spectroscopy. The light-curve morphology and nebular emission lines can be explained by the low explosion energy and neutron-rich nucleosynthesis produced in an electron-capture supernova. This identification provides insights into the complex stellar evolution, supernova physics, cosmic nucleosynthesis and remnant populations in the transitional mass range.

在白矮星形成和铁核坍缩超新星之间的过渡质量范围（约 8-10 个太阳质量）内，预计恒星会产生电子捕获超新星。从理论上讲，这些前身星被认为是具有简并 O + Ne + Mg 核心的超渐近巨分支星，电子捕获到 Ne 和 Mg 原子核上应该会引发核心坍缩^1,2,3,4。然而，还没有明确地从电子捕获起源中识别出超新星，部分原因是理论预测的不确定性。在这里，我们提出了电子捕获超新星的六个指标，并表明超新星 2018zd 是唯一已知的超新星，有强有力的证据或与所有六个指标一致：前身识别、星际物质、化学成分^5,6,7、爆炸能量、光变曲线和核合成^8,9,10,11,12。对于超新星 2018zd，我们根据爆炸前图像中微弱的候选者以及早期紫外颜色和闪光光谱揭示的化学富集的星际物质，推断出超渐近巨星分支祖先。光曲线形态和星云发射线可以用电子捕获超新星产生的低爆炸能量和富含中子的核合成来解释。这一鉴定为复杂的恒星演化、超新星物理学、宇宙核合成和过渡质量范围内的残余种群提供了见解。