Beryllium-8 (⁸Be, Be-8) is a radionuclide with 4 neutrons and 4 protons. It is an unbound resonance and nominally an isotope of beryllium. It decays into two alpha particles with a half-life on the order of 10⁻¹⁶ seconds; this has important ramifications in stellar nucleosynthesis as it creates a bottleneck in the creation of heavier chemical elements. The properties of ⁸Be have also led to speculation on the fine tuning of the Universe, and theoretical investigations on cosmological evolution had ⁸Be been stable.