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Register a new userAppearance of Light Clusters in Post-bounce Evolution of Core-Collapse Supernovae
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We explore the abundance of light clusters in core-collapse supernovae at post-bounce stage in a quantum statistical approach. Adopting the profile of a supernova core from detailed numerical simulations, we study the distribution of light bound clusters up to alpha particles (A=2-4) as well as heavy nuclei (A > 4) in dense matter at finite temperature. Within the frame of a cluster-mean field approach, the abundances of light clusters are evaluated accounting for self-energy, Pauli blocking and effects of continuum correlations. We find that deuterons and tritons, in addition to 3He and 4He, appear abundantly in a wide region from the surface of the proto-neutron star to the position of the shock wave. The appearance of light clusters may modify the neutrino emission in the cooling region and the neutrino absorption in the heating region, and, thereby, influence the supernova mechanism.
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We investigate the post-explosion phase in core-collapse supernovae with 2D hydrodynamical simulations and a simple neutrino treatment. The latter allows us to perform 46 simulations and follow the evolution of the 32 successful explosions during several seconds. We present a broad study based on three progenitors (11.2 $M_odot$, 15 $M_odot$, and 27 $M_odot$), different neutrino-heating efficiencies, and various rotation rates. We show that the first seconds after shock revival determine the final explosion energy, remnant mass, and properties of ejected matter. Our results suggest that a continued mass accretion increases the explosion energy even at late times. We link the late-time mass accretion to initial conditions such as rotation strength and shock deformation at explosion time. Only some of our simulations develop a neutrino-driven wind that survives for several seconds. This indicates that neutrino-driven winds are not a standard feature expected after every successful explosion. Even if our neutrino treatment is simple, we estimate the nucleosynthesis of the exploding models for the 15 $M_odot$ progenitor after correcting the neutrino energies and luminosities to get a more realistic electron fraction.
We study the evolution of supernova core from the beginning of gravitational collapse of a 15Msolar star up to 1 second after core bounce. We present results of spherically symmetric simulations of core-collapse supernovae by solving general relativistic neutrino-radiation-hydrodynamics in the implicit time-differencing. We aim to explore the evolution of shock wave in a long term and investigate the formation of protoneutron star together with supernova neutrino signatures. These studies are done to examine the influence of equation of state (EOS) on the postbounce evolution of shock wave in the late phase and the resulting thermal evolution of protoneutron star. We make a comparison of two sets of EOS, that is, by Lattimer and Swesty (LS-EOS) and by Shen et al.(SH-EOS). We found that, for both EOSs, the core does not explode and the shock wave stalls similarly in the first 100 milliseconds after bounce. The revival of shock wave does not occur even after a long period in either cases. However, the recession of shock wave appears different beyond 200 milliseconds after bounce, having different thermal evolution of central core. A more compact protoneutron star is found for LS-EOS than SH-EOS with a difference in the central density by a factor of ~2 and a difference of ~10 MeV in the peak temperature. Resulting spectra of supernova neutrinos are different to the extent that may be detectable by terrestrial neutrino detectors.
One- (1D) and two-dimensional (2D) core-collapse supernova simulations using full Boltzmann neutrino transport for 11.2M and 15.0M progenitor models have been performed to verify the closure relation for the moment method used in the approximate radiation transfer. This study finds areas where the results of the closure relation are inconsistent with those of Boltzmann transport, even for rotational models. In 1D simulations, the Eddington factors p defined in the fluid rest frame (FR) are compared to evaluate the maximum entropy closure for the Fermi-Dirac distribution (MEFD), confirming that MEFD closure performs better than other closures if p < 1/3 and phase space occupancy e > 0.5. In 2D simulations for non-rotating progenitor models, similar results are obtained from the principal-axis analysis of the Eddington tensor kij measured in FR. However, for rotating progenitor models, the principal axes of kij for Boltzmann transport tilt toward oblique directions where matter and neutrinos move relatively fast in azimuthal directions, while the principal axes of kij for MEFD closure are always parallel or perpendicular to the neutrino flux. Thus, the assumption of axisymmetric angular distribution to the flux direction in the closure relation does not hold in the strongly rotating supernova core in the early post-bounce phase. It is also shown that the deviation of the principal axes of kij from the flux direction increases when evaluated in a laboratory frame (LB). The optically thin and thick terms of the pressure tensor in LB negatively impact results in optically thicker and thinner regions, respectively.
Massive stars (M> 10Msun) end their lives with spectacular explosions due to gravitational collapse. The collapse turns the stars into compact objects such as neutron stars and black holes with the ejection of cosmic rays and heavy elements. Despite the importance of these astrophysical events, the mechanism of supernova explosions has been an unsolved issue in astrophysics. This is because clarification of the supernova dynamics requires the full knowledge of nuclear and neutrino physics at extreme conditions, and large-scale numerical simulations of neutrino radiation hydrodynamics in multi-dimensions. This article is a brief overview of the understanding (with difficulty) of the supernova mechanism through the recent advance of numerical modeling at supercomputing facilities. Numerical studies with the progress of nuclear physics are applied to follow the evolution of compact objects with neutrino emissions in order to reveal the birth of pulsars/black holes from the massive stars.
We report on the core-collapse supernova simulation we conducted for a 11.2 M progenitor model in three-dimensional space up to 20 ms after bounce, using a radiation hydrodynamics code with full Boltzmann neutrino transport. We solve the six-dimensional Boltzmann equations for three neutrino species and the three-dimensional compressible Euler equations with Furusawa and Togashis nuclear equation of state. We focus on the prompt convection at 10 ms after bounce and investigate how neutrinos are transported in the convective matter. We apply a new analysis based on the eigenvalues and eigenvectors of the Eddington tensor and make a comparison between the Boltzmann transport results and the M1 closure approximation in the transition regime between the optically thick and thin limits. We visualize the eigenvalues and eigenvectors using an ellipsoid, in which each principal axis is parallel to one of the eigenvectors and has a length proportional to the corresponding eigenvalue. This approach enables us to understand the difference between the Eddington tensor derived directly from the Boltzmann simulation and the one given by the M1 prescription from a new perspective. We find that the longest principal axis of the ellipsoid is almost always nearly parallel to the energy flux in the M1 closure approximation whereas in the Boltzmann simulation it becomes perpendicular in some transition regions, where the mean free path is 0.1 times the radius. In three spatial dimensions, the convective motions make it difficult to predict where this happens and to possibly improve the closure relation there.
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