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Difficulties in Probing Nuclear Physics: A Study of
Abstract
The nucleosynthetic yield from a supernova explosion depends upon a variety of effects: progenitor evolution, explosion process, details of the nuclear network, and nuclear rates. Especially in studies of integrated stellar yields, simplifications reduce these uncertainties. But nature is much more complex, and to actually study nuclear rates, we will have to understand the full, complex set of processes involved in nucleosynthesis. Here we discuss a few of these complexities and detail how the NuGrid collaboration will address them. 10th Symposium on Nuclei in the Cosmos
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Understanding the nature of the r-process is one of the great unsolved problems in astrophysics. Obtaining accurate nuclear rates will eventually be critical in solving this problem. But to truly take advantage of accurate rates, we must understand the r-process beyond the phenomeno-logical level of postdictive science and move toward predictive models based on calculations anchored by physical models. Using the fallback r-process site, we outline the process of identifying the aspects of this model that are not yet understood and assessing the uncertainties in our lack of understanding. These are the first 2 steps of predictive modeling that can lead to the final step: addressing the aspects that produce the largest uncertainty and minimizing that uncertainty.
We present the results from a series of two-dimensional core-collapse simulations using a rotating progenitor star. We find that the convection in these simulations is less vigorous because a) rotation weakens the core bounce which seeds the neutrino-driven convection and b) the angular momentum profile in the rotating core stabilizes against convection. The limited convection leads to explosions which occur later and are weaker than the explosions produced from the collapse of non-rotating cores. However, because the convection is constrained to the polar regions, when the explosion occurs, it is stronger along the polar axis. This asymmetric explosion can explain the polarization measurements of core-collapse supernovae. These asymmetries also provide a natural mechanism to mix the products of nucleosynthesis out into the helium and hydrogen layers of the star. We also discuss the role the collapse of these rotating stars play on the generation of magnetic fields and neutron star kicks. Given a range of progenitor rotation periods, we predict a range of supernova energies for the same progenitor mass. The critical mass for black hole formation also depends upon the rotation speed of the progenitor. Comment: 16 pages text + 13 figures, submitted to ApJ