Karlheinz Langanke

Carl Friedrich von Weizsäcker published two important papers on topics of nuclear astrophysics in 1937 and 1938 before he turned his attention elsewhere motivated by the discovery of fission and the outbreak of war in 1939. It seems, however, that he continued to actively think about issues related to astrophysics, namely the discussion and role of neutron stars and cosmology. Both are contemporary topics today. This paper presents the development of Weizsäcker’s thoughts in the years between 1935 and 1945, making use of his personal notes and letters.

Despite its amazing quantitative successes and contributions to revolutionary technologies, physics currently faces many unsolved mysteries ranging from the meaning of quantum mechanics to the nature of the dark energy that will determine the future of the Universe. It is clearly prohibitive for the general reader, and even the best informed physicists, to follow the vast number of technical papers published in the thousands of specialized journals. For this reason, we have asked the leading experts across many of the most important areas of physics to summarise their global assessment of some of the most important issues. In lieu of an extremely long abstract summarising the contents, we invite the reader to look at the section headings and their authors, and then to indulge in a feast of stimulating topics spanning the current frontiers of fundamental physics from ‘The Future of Physics’ by William D Phillips and ‘What characterises topological effects in physics?’ by Gerard ’t Hooft through the contributions of the widest imaginable range of world leaders in their respective areas. This paper is presented as a preface to exciting developments by senior and young scientists in the years that lie ahead, and a complement to the less authoritative popular accounts by journalists.

Nuclear processes play an essential role for the evolution of many astrophysical objects and they are key to the origin of the elements in the Universe. Our understanding of the Universe has benefitted from the tremendous progress in nuclear physics which became possible due to novel experimental facilities and improved instrumentation as well as due to advances in theoretical modelling. The talk exemplifies this progress for three selected topics: solar and stellar hydrostatic burning, neutron-star mergers as a site of heavy-element production by the r-process and the influence of electron capture on nuclei for the core-collapse in massive stars leading to supernova explosions.

The astrophysical r-process produces about half of the elements heavier than iron in the Universe and all of the transactinides. Recently neutron star mergers have been identified as one site of r-process nucleosynthesis. Simulations of this site and the associated nucleosynthesis requires essential nuclear input, ranging from the Equation of State (EoS) of nuclear matter at extreme densities and temperatures to the properties of very neutron-rich nuclei. Many of these quantities have to be modeled, however, constrained by a steadily increasing amount of experimental data. This manuscript summarizes the knowledge of nuclear input required for r-process studies in neutron star mergers.

The production of about half of the heavy elements found in nature is assigned to a specific astrophysical nucleosynthesis process: the rapid neutron capture process (r-process). Although this idea has been postulated more than six decades ago, the full understanding faces two types of uncertainties/open questions: (a) The nucleosynthesis path in the nuclear chart runs close to the neutron-drip line, where presently only limited experimental information is available, and one has to rely strongly on theoretical predictions for nuclear properties. (b) While for many years the occurrence of the r-process has been associated with supernovae, more recent studies have cast substantial doubts on this environment. Alternative scenarios include the mergers of neutron stars, neutron-star black hole mergers, but possibly also rare classes of supernovae as well as hypernovae/collapsars with polar jet ejecta and also accretion disk outflows related to the collapse of fast rotating massive stars with high magnetic fields. Stellar r-process abundance observations, have provided insights into, and constraints on the frequency of and conditions in the responsible stellar production sites. One of them, neutron star mergers, was just identified and related to the Gravitational Wave event GW170817. High resolution observations, increasingly more precise due to improved experimental atomic data, have been particularly important in defining the heavy element abundance patterns of the old halo stars, and thus determining the extent, and nature, of the earliest nucleosynthesis in our Galaxy. Combining new results and important breakthroughs in the related nuclear, atomic and astronomical fields of science, this review attempts to provide an answer to the question "How Were the Elements from Iron to Uranium Made?" (Abridged)

Neutrino reactions on nuclei play important roles for the dynamics of supernovae and their associated nucleosynthesis. This manuscript summarizes the current status in deriving the relevant cross sections for supernova neutrinos and discusses the importance of neutrino-nucleus reactions for supernova nucleosynthesis. In particular we report on the first study of neutrino nucleosynthesis which consistently considers time-dependent spectra for all neutrino flavors as predicted by supernova simulations.