Deuterium in the Galaxy.

Deuterium in the universe is thought to have been formed in the initial fireball of the big bang. Because deuterium abundances is a sensitive function of baryon density (considered a clue to the size of the cosmos), its measurement could shed light on the universe's ultimate density, i.e., whether or not there is enough matter present to halt the present expansion through gravitational collapse. This paper outlines attempts to measure galactic deuterium abundance, especially by an analysis of Lyman lines in the UV spectra.