Songaila A, Wampler E J, Cowie L L
Institute for Astronomy, University of Hawaii, Honolulu 96822, USA.
Nature. 1997 Jan 9;385(6612):137-9. doi: 10.1038/385137a0.
Intergalactic gas clouds at high redshifts have element abundances that are close to primordial. The ratio of deuterium to hydrogen (D/H) within such clouds-which is determined from absorption lines in the spectra of more distant quasars that lie along the same line of sight-provides the best estimate of the density of baryons (omegaB) in the Universe. Previous estimates of D/H in the early Universe have yielded values that differ by about an order of magnitude, with the lower values implying a high density of baryons that may be difficult to reconcile with both estimates of the primordial abundances of other light elements (especially 4He) and the known number of light neutrinos. The accuracy of such D/H determinations is heavily dependent on the inferred column density of neutral hydrogen in the absorbing clouds. Here we report an independent measurement of the neutral hydrogen column density in the cloud towards the quasar Q1937 - 1009, for which one of the low D/H values was derived. Our measurement requires a substantial revision to the D/H value reported previously; we obtain a lower limit of D/H > 4 x 10(-5) for this cloud, which implies omegaB < 0.016 for a Hubble constant of 100 km s(-1) Mpc(-1). This reduced upper limit for the baryon density relieves any conflict with standard Big Bang nucleosynthesis.
高红移的星系际气体云具有接近原初的元素丰度。此类云团中氘与氢的比率（D/H）——由沿同一视线方向的更遥远类星体光谱中的吸收线确定——为宇宙中重子密度（ΩB）提供了最佳估计。先前对早期宇宙中D/H的估计得出的值相差约一个数量级，较低的值意味着重子密度较高，这可能难以与其他轻元素（尤其是4He）的原初丰度估计值以及已知的轻中微子数量相协调。此类D/H测定的准确性在很大程度上取决于吸收云中中性氢的推断柱密度。在此，我们报告了对朝向类星体Q1937 - 1009的云团中中性氢柱密度的独立测量，之前就是从该云团得出了一个较低的D/H值。我们的测量要求对先前报告的D/H值进行大幅修正；对于该云团，我们得到D/H > 4×10⁻⁵的下限，这意味着对于100 km s⁻¹ Mpc⁻¹的哈勃常数，ΩB < 0.016。重子密度的这个降低的上限消除了与标准大爆炸核合成的任何冲突。
