Periodic Reporting for period 4 - EUROPIUM (The origin of heavy elements: a nuclear physics and astrophysics challenge)
Période du rapport: 2020-11-01 au 2021-10-31
The EUROPIUM project addresses the exciting question: Where and how are heavy elements synthesized in the universe? While hydrogen and helium were already produced in the Big Bang at the beginning of the universe, all other elements have formed in stars. During their quiet life, stars produce elements up to iron through hydrostatic nuclear burning. All elements heavier than iron are synthesized by neutron capture processes. In EUROPIUM, we have investigated the rapid neutron capture process (r-process) that occurs in some core-collapse supernovae and in neutron star mergers. The r-process produces half of the heavy elements from iron to bismuth and it is the only possibility to synthesize uranium and thorium in the universe. In August 2017, there was the first direct observation of the r-process after the detection of gravitational waves from the merger of two neutron stars (GW170817). The radioactive neutron-rich nuclei that are produced by the r-process in neutron star mergers trigger an electromagnetic counterpart. In 2010, we made the first theoretical prediction of this event and named it kilonova. With this discover a new multi-messenger era has just started and the EUROPIUM group has made critical contributions.
The main objective of EUROPIUM was to determine the role of core-collapse supernovae and neutron star mergers in the chemical history of the universe and advance our understanding of the origin of heavy elements by combining hydrodynamical simulations, nucleosynthesis calculations, and observations. Therefore, the group worked in various interdisciplinary directions covering astrophysics, observations, and nuclear physics.
EUROPIUM conclusion is that the heavy elements in the universe are produced by neutron star mergers and magneto-rotational supernovae. Combining hydrodynamical simulations and nucleosynthesis, we were able to use observations to constrain the origin of heavy elements in our galaxy, in surrounding dwarf galaxies, and in our solar system. In our galaxy we showed the need of an early r-process to explain abundances observed. In addition, we have performed simulations with accurate neutrino transport of magneto-rotational supernovae and our nucleosynthesis results shows that the r-process occurs in such events and could explain the observed early r-process. In dwarf galaxies, we have discovered new stars and named them Europium stars as they are the most r-process rich stars ever observed and thus can help to constrain the origin of heavy elements. The heavy elements in our solar system were probably originated in the late disk ejecta from neutron star mergers as we presented in Science. This work critically shows the importance of reducing nuclear physics uncertainties to be able to use observation to constrain the astrophysical environment where heavy elements are produced.
The main objective of EUROPIUM was to determine the role of core-collapse supernovae and neutron star mergers in the chemical history of the universe and advance our understanding of the origin of heavy elements by combining hydrodynamical simulations, nucleosynthesis calculations, and observations. Therefore, the group worked in various interdisciplinary directions covering astrophysics, observations, and nuclear physics.
EUROPIUM conclusion is that the heavy elements in the universe are produced by neutron star mergers and magneto-rotational supernovae. Combining hydrodynamical simulations and nucleosynthesis, we were able to use observations to constrain the origin of heavy elements in our galaxy, in surrounding dwarf galaxies, and in our solar system. In our galaxy we showed the need of an early r-process to explain abundances observed. In addition, we have performed simulations with accurate neutrino transport of magneto-rotational supernovae and our nucleosynthesis results shows that the r-process occurs in such events and could explain the observed early r-process. In dwarf galaxies, we have discovered new stars and named them Europium stars as they are the most r-process rich stars ever observed and thus can help to constrain the origin of heavy elements. The heavy elements in our solar system were probably originated in the late disk ejecta from neutron star mergers as we presented in Science. This work critically shows the importance of reducing nuclear physics uncertainties to be able to use observation to constrain the astrophysical environment where heavy elements are produced.
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.
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.
The uniqueness of EUROPIUM is the combination of three fields: 1) hydrodynamic simulations of neutron star mergers and core-collapse supernovae, 2) nucleosynthesis calculations, 3) observations. This has allowed us to advance beyond state-of-the-art as in the following examples:
- First 3D, full general relativity, magneto-hydrodynamic supernova simulations with accurate neutrino transport.
- Nucleosynthesis calculation based on MRSN simulation that included accurate neutrino transport for the first time and thus provided reliable and complete nucleosynthesis.
- Discovery of Europium stars in the dwarf galaxy Fornax. These stars have the highest abundances of r-process ever observed and can be used to track the r-process of single events.
- Combination of meteorite abundances, galactic chemical evolution, and nucleosynthesis including astrophysics and nuclear physics uncertainties to determine the r-process site that made the last contribution before our solar system forms and thus explain the origin of heavy elements around us.
- We contributed to find Strontium in the kilonova spectrum and this is the first direct observation of a freshly synthesis r-process element ever observed and the only unambiguous element that could be identify in the kilonova spectrum until now.
- First 3D, full general relativity, magneto-hydrodynamic supernova simulations with accurate neutrino transport.
- Nucleosynthesis calculation based on MRSN simulation that included accurate neutrino transport for the first time and thus provided reliable and complete nucleosynthesis.
- Discovery of Europium stars in the dwarf galaxy Fornax. These stars have the highest abundances of r-process ever observed and can be used to track the r-process of single events.
- Combination of meteorite abundances, galactic chemical evolution, and nucleosynthesis including astrophysics and nuclear physics uncertainties to determine the r-process site that made the last contribution before our solar system forms and thus explain the origin of heavy elements around us.
- We contributed to find Strontium in the kilonova spectrum and this is the first direct observation of a freshly synthesis r-process element ever observed and the only unambiguous element that could be identify in the kilonova spectrum until now.