3D Explosion Modeling
While state-of-the-art simulations in two dimensions (2D) can basically confirm the viability of the neutrino-driven mechanism and the supportive role of non-radial hydrodynamical instabilities (Press release Februar 2009), the resulting explosions tend to be underenergetic in comparison to observations. Furthermore, the artificial assumption of rotational symmetry leads to torus-like flow structures in conjunction with unipolar or dipolar deformations along the azimuthal symmetry axis, and an inversion of the turbulent energy cascade distributing the energy from the smallest to the largest scales in an unphysical way is found. This is in contrast to the “real“ situation in three spatial dimensions (3D) and underlines the need for 3D simulations in order to represent core-collapse supernovae by explosion models as realistically as possible.
With the advent of the first fully self-consistent 3D simulations, a dilemma emerged: Until recently, despite being more realistic without an artificially imposed symmetry axis, 3D models have not shown successful explosions as opposed to their 2D counterparts. But they still revealed new physical phenomena taking place in the collapsing core that had not been observed in 2D simulations (Press Release 2013 and Highlight 2014). During the past months, research efforts fostered and supported by the ERC Advanced Grant led to a major breakthrough in the understanding of core-collapse supernovae. With the currently most complete description of neutrino interactions with matter in a supernova calculation, the Garching group could present the first successful, neutrino-driven explosion of a star with an initial mass of 9.6 solar masses in a self-consistent simulation in 3D (Fig. 1). The simulation shows that turbulence in 3D helps to explode the star and results in an explosion energy that is about 10% higher than in the corresponding 2D simulation (Highlight April 2015). In addition to the 9.6 solar-mass case, the Garching group also obtained a successful 3D explosion of a 20 solar-mass progenitor (Fig. 2, Highlight August 2015). Within the uncertainties that still exist with respect to the complex neutrino reactions taking place in the newly born neutron star, these two models clearly demonstrate that the energy provided by the neutrinos can in fact revive the previously stalled shock front, proving the operability of the neutrino-driven mechanism in 3D.
Due to the enormous computational demands of neutrino transport and interactions, self-consistent simulations of core-collapse supernovae in 3D range at the limits of the resources provided by current supercomputers for scientific research projects. Thanks to ample computer time by the “Partnership for Advanced Computing in Europe (PRACE)“, the two 3D simulations could be performed on 16,000 cores on the supercomputers “SuperMUC“ at the Leibniz Rechnzentrum (LRZ) in Garching and “MareNostrum“ at the Barcelona Supercomputing Center (BSC). For an evolution up to half a second after explosion, typically 50 million core hours and several months of computation time are needed for each model. With additional computing time granted by the “Gauss Centre of Supercomputing“, the Garching group aims at a further consolidation of the theoretical knowledge concerning the explosion mechanism of core-collapse supernovae. On the one hand, the resolution of current 3D models has to be improved in order to fully resolve the turbulent energy cascading and finally probe the efficiency of turbulent effects. On the other hand, the influence of additional parameters on the explosion physics that have not been studied in detail so far has to be investigated. This includes the effect of stellar rotation as well as the role of initial conditions in the pre-collapse cores (3D progenitor modeling).