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yexuqing木虫之王 (文学泰斗)
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寻找附近宇宙中的锂-7同位素
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寻找附近宇宙中的锂-7同位素 Nature 489 (7414) 发表日期：2012年9月6日 原始宇宙中锂-7同位素的预测丰度是“银晕”恒星大气中实测丰度的四倍，但难以对银河系中的这一同位素进行追踪，因为它大部分可能已经燃烧掉了。这篇论文报告了在银河系以外一个附近星系“小麦哲伦云”的低金属空气中对星际锂的探测结果。这一星系中今天的锂-7丰度与有关“大爆炸”核合成的标准理论的预测结果几乎相同，尽管这些数据也可与非标准模型调和。 doi: 10.1038/nature11407 http://www.nature.com/nature/jou ... pdf/nature11407.pdf Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud J. Christopher Howk,1 Nicolas Lehner,1 Brian D. Fields2, 3 & Grant J. Mathews1 Affiliations Contributions Corresponding author Journal name: Nature Volume: 489, Pages: 121–123 Date published: (06 September 2012) DOI: doi:10.1038/nature11407 Received 01 June 2012 Accepted 16 July 2012 Published online 05 September 2012 The primordial abundances of light elements produced in the standard theory of Big Bang nucleosynthesis (BBN) depend only on the cosmic ratio of baryons to photons, a quantity inferred from observations of the microwave background1. The predicted2, 3, 4 primordial 7Li abundance is four times that measured in the atmospheres of Galactic halo stars5, 6, 7. This discrepancy could be caused by modification of surface lithium abundances during the stars’ lifetimes8 or by physics beyond the Standard Model that affects early nucleosynthesis9, 10. The lithium abundance of low-metallicity gas provides an alternative constraint on the primordial abundance and cosmic evolution of lithium11 that is not susceptible to the in situ modifications that may affect stellar atmospheres. Here we report observations of interstellar 7Li in the low-metallicity gas of the Small Magellanic Cloud, a nearby galaxy with a quarter the Sun’s metallicity. The present-day 7Li abundance of the Small Magellanic Cloud is nearly equal to the BBN predictions, severely constraining the amount of possible subsequent enrichment of the gas by stellar and cosmic-ray nucleosynthesis. Our measurements can be reconciled with standard BBN with an extremely fine-tuned depletion of stellar Li with metallicity. They are also consistent with non-standard BBN. |
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