The cosmic origin and evolution of the elements

The origin of many elements of the periodic table remains an unsolved problem. Many nucleosynthetic channels are broadly understood, mostly those involving the quiescent stellar evolution phases that can be reliably modeled in spherical symmetry. However, significant uncertainties remain regarding our understanding of certain groups of elements, such as the intermediate and rapid neutron-capture processes, the p-process, or the origin of odd-Z elements in the most metal-poor stars. Beyond completing our understanding of the origin of the elements, nuclear astrophysics aims to provide reliable predictions for when, where, and which elements are released from dying stars. Coupled with galactic and extragalactic observations of stellar abundances, this approach, known as galactic archaeology, can provide key insights into how galaxies form and evolve. However, the predictive power and fidelity of our simulations are in many cases insufficient to fully deliver on this vision, partly due to the intrinsically three-dimensional (3D) nature of the stellar processes involved. Only recently can dynamic events in the evolution of massive stars be tracked with high-fidelity, 3D hydrodynamic simulations; these have already led to scenarios that can explain the origin of odd-Z elements. Also, asteroseismology is emerging as a powerful tool to validate these new stellar models which will ultimately create 3D progenitors for 3D supernova explosion simulations that are key to understanding the diverse nature of supernova remnant and stellar abundance observations. On the observational side, the detection in 2017 of a neutron star merger in gravitational waves started the era of multi-messenger gravitational wave astronomy, with multi-wavelength follow-up of that event resulting in the confirmation of neutron star mergers as sites for the rapid neutron capture process, given the broad agreement with theoretical predictions. Since then, gravitational wave observatories have improved in sensitivity, yielding a higher rate of detections. This trend will continue to increase as future upgrades and new facilities come online. Larger sample sizes will test our understanding of these events, requiring reliable predictions, which are computationally very challenging. Emerging and future multi-wavelength surveys are delivering large data sets of stellar abundances. These have the potential to provide a new window into galactic formation and evolution processes, if they can be paired with reliable stellar yield models. A key element to fulfill this vision is to address the substantial uncertainties in modeling the stellar atmospheres required to determine abundances reliably. Here, 3D hydrodynamic and non-LTE effects still again provide major challenges. Unraveling the origin of the elements in the context of galaxy formation and evolution requires, on the Astrophysics side, the interplay between observations of stellar abundances in large surveys, detailed studies of individual objects such as supernova remnants, multi-messenger transient follow-up, new generation of 3D hydrodynamic stellar evolution models, and simulations of explosive events using neutrino radiation-magnetohydrodynamics in numerical relativity with nuclear processes. A key ingredient to interpreting observations and generating theoretical predictions is a wide array of fundamental nuclear data properties, such as nuclear reaction cross sections and the equation of state at high densities. For much of the nuclear data of unstable species required, however, only theoretical predictions are available. Experiments with unstable (rare) isotope beams are now becoming possible in the regime relevant to address this critical nuclear data need. Nuclear astrophysics is therefore an interdisciplinary research frontier that integrates all of these sub-fields of Astrophysics and Experimental Physics. Sustaining Canadian leadership on the observational side in the next decade will require access to transient and non-transient surveys like LSST, SKA, or MSE, support for target-of-opportunity observing in current and future Canadian telescopes, and participation in next-generation X-ray telescopes such as ATHENA. On the theory side, state-of-the-art predictions for the next decade will require an ambitious succession to the Niagara supercomputer to support large parallel jobs. The lack of funding for postdoctoral researchers and of funding envelopes for such an interdisciplinary collaboration prevents Canadian scientists from competing on a level-playing field with international groups, as existing funding programs do not meet the needs of the field. We propose a funding instrument for postdoctoral training that reflects the interdisciplinary nature of nuclear astrophysics research. We also propose the creation of a national collaborative funding program that allows for joint projects and workshop organization, increasing ties between these communities.

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