Numerical models of core-collapse supernovae have matured greatly over the past few decades. With impressive accuracy, they now couple relativistic gravity, magnetohydrodynamics, nuclear physics, and neutrino transport. Neutrinos, copiously produced in the collapsed core, are the main driver of most of these supernovae. Neutrino oscillations are probably the most crucial ingredient that is still missing from the majority of models, even though their presence and possible importance have long been suggested. The reason for this gap in modeling is twofold: Many relevant physical parameters are poorly known, and the most important oscillation processes are very difficult to simulate. Now Ryuichiro Akaho at Waseda University in Japan and colleagues have made a key step toward a self-consistent model and revealed some complexities that arise when incorporating neutrino oscillations [1].
Stars are supported against their own gravity primarily by gas pressure, which is maintained by exothermic nuclear reactions. In high-mass stars, nuclear burning starts with the fusion of hydrogen into helium and continues through progressively heavier elements until the core is dominated by iron-group nuclei, at which point fusion no longer releases energy. Pressure support then no longer suffices to stabilize the core, and it collapses to a protoneutron star, a hot compact object with about 1.5 solar masses concentrated in a radius of a few tens of kilometers. During the collapse, a shock wave forms at this object’s surface and stalls after propagating outward for only about 100 km (Fig. 1). Neutrinos generated in and around the protoneutron star can heat the surrounding gas, increasing its energy.