The work of EUROPIM aligns along three main topics that are strongly connected: neutron star mergers, core-collapse supernovae, and nucleosynthesis.
In the EUROPIUM project, we have shown the richness of the neutron star merger nucleosynthesis and the importance to account for the late disk ejecta that may has been the origin of r-process elements in our solar system (see our Science publication in 2021). By combining nucleosynthesis, observations and galactic chemical evolution, we could also demonstrate that there is an additional early contribution to r-process elements and this can be explained by rare supernovae driven by strong magnetic fields, magneto-rotational supernovae (MRSN). We have presented the first full general relativity, 3D simulations for MRSN including detail neutrino transport as well as the first nucleosynthesis study for several 2D supernova simulations with magnetic fields and accurate neutrino transport. The latter is critical to account for the whole nucleosynthesis.
Core-collapse supernovae driven by neutrinos contribute to the production of lighter heavy elements between Strontium and Silver. We have performed hydrodynamic simulations of these event and demonstrated that the neutron star contraction is ruled by the effective mass that controls the thermal contribution to the equation of state. Moreover, the impact and uncertainties due to different neutrino transport were analyzed for the first time based on the same hydrodynamic code. At the end of the project, we were able to provide 32 exploding models following the evolution for seconds after the explosion. This study probes the importance of late accretion to explain the observed explosion energy and nucleosynthesis. Moreover, we showed that the neutrino-driven wind is not a standard feature and develops only rarely when the mass accretion is very low. EUROPIUM has also achieved to provide the first complete nucleosynthesis study of the weak r-process considering astrophysics and nuclear physics uncertainties. Our work has motivated and supported experiments worldwide to measure (alpha, n) reactions and will have a big impact in future nuclear astrophysics experimental programs in new nuclear physics facilities.
EUROPIUM nucleosynthesis studies included broad variability of astrophysical conditions and environments as well as many nuclear physics models for nuclear masses, beta decays, and fission. This allowed us to calculate uncertainties and compare to observations. Two highlights are our comparison to Actinides boost stars and our discovery of Europium stars. Both demonstrates the potential of observations to constrain the astrophysics sites where heavy elements are produced and the importance of reducing the nuclear physics uncertainties by future experiments and improved theoretical models.
Our results have been published in several refereed journals including Science and Nature and presented in workshops, conferences, seminars, and colloquia worldwide. Several members of the group have contributed to an important and complete review about the r-process. The EUROPIUM project has been also presented to the general public in outreach talks and press releases, for example in an article in the Physik Journal and a talk at the AAAS meeting in 2019.
