Abstract
Nuclear reactions shape the life and death of stars and they produce most of the chemical elements in the Universe. The cross section, at the energy of the Gamow peak, is a crucial ingredient to improve our knowledge on stellar and Universe chemical evolution. Its low value at stellar energies prevent direct measurements in earth-based laboratories. In recent years low energy data significantly improved thanks to underground facilities, pioneered by the Laboratory for Underground Nuclear Astrophysycs (LUNA). LUNA started its activity in 1991 with a 50 kV electrostatic accelerator installed under Gran Sasso, which is a natural shield against cosmic rays ensuring a ultra low background environment. LUNA early activity was dedicated to reactions relevant to the Sun, and then, thanks to the installation of a new accelerator (LUNA400), it focused on the study of the Big Bang Nucleosynthesis (BBN) and of the CNO, NeNa and MgAl cycles. LUNA is now facing the next steps, helium and carbon burning, thanks to the new 3.5MV accelerator, which has just started its activity at the Bellotti Facility of LNGS. The accelerator provides hydrogen, helium and carbon beams, allowing to study the reactions that shape both the evolution of massive stars to their final fate and the synthesis of most of the elements in the Universe.