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FaInt Supernovae and Hypernovae: Mechanism and Nucleosynthesis

Final Report Summary - FISH (FaInt Supernovae and Hypernovae: Mechanism and Nucleosynthesis)

The project includes subprojects which range from experimental and theoretical nuclear physics with relation to (i) the nuclear equation of state (required for the collapse of matter to highest densities, possibly permitting the collapse to a black hole); (ii) nuclear reactions (permitting to follow the energy generation in explosions and the prediction of the elemental and isotopic ejecta composition); over particle physics with relation to (iii) neutrino-matter interactions, neutrino oscillations and the related neutrino (radiation) transport; late stages of stellar evolution with rotation and magnetic fields leading to (iv) general-relativistic magneto-hydrodynamic simulations of core collapse and compact object mergers; up to (v) specific nucleosynthesis predictions for the ejecta of such events, plus their impact in the chemical evolution of galaxies in close contact with astronomical observers.
Thus, this inter- and cross-disciplinary approach addresses the formation and mergers of compact objects, accompanied by explosive events whose ejecta play a key role in the evolution of galaxies.
We have provided essential aspects of the input physics: (1) a data base of nuclear equations of state in agreement with present knowledge from nuclear physics and astronomical observations (https://astro.physik.unibas.ch/people/matthias-hempel/equations-of-state.html and http://compose.obspm.fr) (2) a data base of nuclear reactions across the nuclear chart (3 the isotropic diffusion source approximation (IDSA) code for multi-dimensional neutrino transport on our webpage (https://astro.physik.unibas.ch/people/matthias-liebendoerfer/download.html). A detailed code comparison for (4) magneto-hydrodynamic simulations of core collapse with an SPH code (SPHINX), the open source grid-based code FLASH, our 3D MHD code FISH, and the general relativistic code M1 has been performed, analyzing in which regime which treatment is suited best, which led to extended production runs for such collapse calculations. (5) Nucleosynthesis predictions for magnetars have been obtained with varying rotation rates and magnetic fields. Similar investigations have been done for neutron star mergers. (6) The results have been implemented to predict the dust composition originating from such events and (7) to understand the temporal evolution of the heaviest elements during the evolution of galaxies and whether they are in agreement with astronomical observations.

A major achievement was to understand the fate of massive stars and the dividing line between supernova explosions and black hole formation, with an intermediate range leading to faint supernovae. One interesting point is that the initial (somewhat spherically symmetric) expectation that fallback plays a major role after an apparent initially successful explosion, is incorrect. In multi-D simulations the “fallback” is rather a continuous process, causing increasingly weaker explosions up to the point of black hole formation. This behavior is mirrored in our effective 1D simulations which reproduces the observed trend in explosion energies and 56Ni ejecta. Our present investigations show - up to now - only the regular core-collapse supernova branch and the “faint” branch. While we undertook extensive collapse simulations with varying rotation and magnetic fields, causing in extreme cases polar jets and central magnetars with magnetic fields of 10^15 Gauss (and the formation of large amounts of heavy elements), we were not yet successful in following up on black hole formation events with fast rotation and high magnetic fields in their post collapse phase. These events are expected to lead to hypernovae and long duration Gamma-Ray Bursts. Such investigations are still under way. The recent observations of electromagnetic counterparts of short duration Gamma-Ray Bursts and the detection of gravitational waves from compact binary mergers made us shift gears in that direction. We were highly successful in neutron star merger simulations, causing short duration Gamma-Ray Bursts, strong gravitational wave emission, and the ejection of the heaviest elements.