Lithium abundance at the formation of the Galaxy

The observed abundance of lithium in population I stars (young stars)¹ seems to have been stable during the past 5 × 10⁹ yr (ref. 2). This stability has been used previously^1,3 to estimate the abundance of lithium at the time of formation of the Galaxy and at pre-galactic times^1,3. But because the basis for this estimate was not completely satisfactory, we have made new observations, aiming at a better determination of the lithium abundance at the time of formation of the Galaxy. The newly observed stars are extreme population II dwarfs (very old, very metal-poor stars). Their lithium abundance turned out to be significantly lower than the abundance in population I stars. If attributed to the big bang, this lithium abundance suggests a rather low baryonic density of the Universe, which in turn favours, under some assumptions, an open Universe³. Finally, we suggest that the good agreement between the abundance of ⁷Li and the deuterium ²H abundance³ supports the standard model of the big bang.