Tytler D, Fan X M, Burles S
Department of Physics, University of California, San Diego, La Jolla, 92093-0111, USA.
Nature. 1996 May 16;381(6579):207-9. doi: 10.1038/381207a0.
The primordial ratio of deuterium to hydrogen nuclei (D/H), created as a result of the Big Bang, provides the most sensitive measure of the cosmological density of baryons. Measurements of the D/H ratio in the interstellar medium of our Galaxy place a strict lower limit on the primordial ratio, because processing of gas by stars reduces the abundance of deuterium relative to hydrogen. Absorption of radiation from distant quasars by intervening clouds of gas offers a means of probing D/H ratios at large redshifts, where the effects of stellar processing should be negligible. Measurements on one absorption system have indicated an extremely high primordial abundance ratio of 24 x 10(-5). Here we report a measurement of the D/H ratio in another high-redshift absorption system, and obtain a value that is an order of magnitude lower than that reported previously. The measured ratio of 2.3 x 10(-5) is consistent with that in the interstellar medium (after allowing for Galactic chemical evolution), and indicates that the absorption spectra on which the earlier estimates are based may have been subject to strong contamination. We calculate a baryon density that is 5% of the critical density required to close the Universe.
由大爆炸产生的氘与氢原子核的原始比率（D/H），是重子宇宙学密度最灵敏的量度。对我们银河系星际介质中D/H比率的测量为原始比率设定了严格的下限，因为恒星对气体的加工会降低氘相对于氢的丰度。来自遥远类星体的辐射被居间气体云吸收，提供了一种探测大红移处D/H比率的方法，在那里恒星加工的影响应该可以忽略不计。对一个吸收系统的测量表明原始丰度比率极高，为24×10⁻⁵。在此我们报告对另一个高红移吸收系统中D/H比率的测量结果，得到的值比先前报告的值低一个数量级。测得的2.3×10⁻⁵的比率与星际介质中的比率一致（考虑到银河系化学演化后），这表明早期估计所依据的吸收光谱可能受到了严重污染。我们计算出的重子密度是使宇宙闭合所需临界密度的5%。
