Lithium problem solved…almost

Lithium has proved to be a stubborn problem for astrophysicists; the quantities predicted to have resulted from the Big Bang are not present in stars, but the figures have recently been proven correct. Lithium is one of the first three elements to have formed – even before the first stars – through primordial nucleosynthesis. When the Universe was only a few minutes old, neutrons and protons merged to form not only lithium, but hydrogen and helium too. Observations of lithium-6 in metal poor stars suggest this isotope was produced in large quantities during Big Bang nucleosynthesis, but the reaction has never been measured inside the Big Bang nucleosynthesis energy range. A team from the Helmholtz Zentrum Dresden Rossendorf (HZDR) have recently measured this for the first time in experiments conducted at LUNA, Gran Sasso. Scientists used LUNA (Laboratory for Underground Nuclear Astrophysics) to reproduce the nucleosynthesis of lithium by firing helium nuclei at deuterium in order to reach energies similar to those just after the Big Bang. They then measured how much lithium formed and confirmed the theoretical predictions, which differ to the observed lithium concentrations found in the Universe. “For the first time, we could actually study the lithium-6 production in one part of the Big Bang energy range with our experiment,” said Daniel Bemmerer, who has also study the production of lithium-7. The research, published in Physical Review Letters, states: we report on the results of the first measurement of the ²H (?,?)Li⁶ cross section at big bang energies…The primordial ⁶Li/⁷Li isotopic abundance ratio has been determined to be (1.5±0.3)×10^?5, from our experimental data and standard BBN theory.” Even with these new results, the lithium problem still remains a tough one to solve.  Laboratory results suggest the theory of primordial nuceosynthesis is correct, but observations show only half as much lithium-7 as predicted. “Should unusual lithium concentrations be observed in the future, we know, thanks to new measurements, that it cannot be due to the primordial nucleosynthesis,” Bemmerer added. First Direct Measurement of the ²H (?,?) ⁶Li Cross Section at Big Bang Energies and the Primordial Lithium Problem