Improving our understanding of this process is one of the key challenges in nuclear astrophysics. In binary stars, nova explosions can occur when material from one star falls onto the surface of its companion. When temperatures and densities become high enough, protons react with unstable nuclei before they can decay, in a process known as the hot CNO cycle. Studies of key reactions in this sequence will be one of the important thrusts of laboratory nuclear astrophysics for the next several years. Most of these reaction studies require the use of radioactive beam facilities.
Massive stars end their lives in spectacular explosions known as supernovas.
There follows a trampoline-like rebound that sends a shock wave propagating outward. The core, heated by its gravitational collapse, then cools by emitting neutrinos. Great progress has recently been made in understanding how the shock wave, the interaction of the neutrinos with matter outside the core, and the convection induced by this neutrino heating combine to create the supernova explosion. One important goal of nuclear astrophysics is to combine laboratory measurements of nuclear properties and supernova theory to predict the observed abundances of heavy elements. Many of the heavy nuclei, including all the transuranic elements, are made by the rapid capture of neutrons produced in great numbers.