The transport of nuclear reaction products from their sources through the interstellar and intergalactic medium also is unclear. Additionally, many nuclei that are involved in cosmic nuclear reactions are unstable and may only exist temporarily in cosmic sites, and their properties (e.g., binding energy) cannot be investigated in the laboratory due to difficulties in their synthesis. Similarly, stellar structure and its dynamics is not satisfactorily described in models and hard to observe except through asteroseismology, and supernova explosion models lack a consistent description based on physical processes, and include heuristic elements. Current research extensively utilizes computation and numerical modeling.