Cosmic Deuterium

Physics – Nuclear Physics

Scientific paper

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Scientific paper

The knowledge of the primordial deuterium to hydrogen ratio provides one of the most reliable tests of the early Universe nucleosynthesis models and a direct estimate of the cosmic baryon density. Evaluations have been traditionally made using D/H estimations in the interstellar medium, extrapolated backwards in time with the use of galactic evolution models. Direct primordial D/H measurements have been carried out only recently in the direction of quasars. These measurements of deuterium abundances along with observations made in the solar system and in the interstellar medium are presented.New results that indicate spatial variations of the deuterium abundance in the interstellar medium at the level of ~ 50% over scales possibly as small as ~ 10 pc, may question our global vision of deuterium evolution until the causes of the origin of these variations are understood. With a conservative point of view, observations thus suggest that the primordial D/H value should be within the range 1. × 10-5 -3. × 10-4, leading to a relatively low baryon content Universe.Since the actual evolution of deuterium from primordial nucleosynthesis to now is not known in details, more observations, hopefully to be made with the Hubble Space Telescope, FUSE the Far Ultraviolet Spectroscopic Explorer (launched in 1999), or from the ground with the largest telescopes (Keck, VLT, ...), should reveal the evolution of that key element, and better constrain its primordial abundance

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