Rod-Shaped Nuclei

Rod-shaped nuclei, even slablike nuclei, might occur amid the cataclysm of a supernova. This is when nuclear matter---normally hard, spherical, and dense (3 x 10¹⁴ g/cm³)---can thin out, to an average density only half that of normal nuclear matter. The nuclear “rods” would still be densely packed in the star (like a liquid crystal) and the rods might coalesce into slabs, says Gentaro Watanabe, temporarily at the NORDITA lab in Denmark.

He and his colleagues at the Japan Atomic Energy Research Institute, the University of Tokyo, the RIKEN lab, and Keio University, have modeled alternative nuclear shapes in an effort to address the subtle problems in simulating supernovae. One of these problems is that shock waves stall in the stellar core. The Japanese researchers expect that incorporating effects of "pasta" phases (the collective name for rod or slab nuclei) in core collapse simulations would help them to model the explosion more realistically.

The "pasta" phases would be formed in the central region of the collapsing core, while the region where the shock waves propagate and stall is much further out. Neutrinos from central region contribute "neutrino heating" and would help the shock waves to revive. This scenario is more tenable if the pasta phases are present, and not just uniform nuclear matter. (Watanabe et al., Physical Review Letters, 28 January 2005; contact, gentaro@nordita.dk )