And that’s potentially a big deal, given that the neutrinos’ interactions with matter are influenced by their identity. “By modifying the relative spectra of electron neutrinos, electron antineutrinos, and heavy-lepton neutrinos,” the paper’s authors write, “[flavor oscillation] affects charged-current heating and cooling in the region behind the shock.”
The actual physics here is incredibly complicated, since the momentum of each neutrino will vary, as will where they are created relative to the center of the star. This will influence how far they can travel before experiencing a flavor oscillation and how many times they oscillate within the star. The researchers involved here, Mariam Gogilashvili and Irene Tamborra of the University of Copenhagen, aren’t going for a physically exacting model of all of this complexity.
Instead, the two researchers use a simplified model where flavor changes occur roughly instantaneously, and the energy carried by neutrinos is divided evenly among the six types of neutrinos (electron, muon, tau, and their antiparticles). They apply this division of energy in their model as neutrinos travel through the space between the star’s core (where neutrinos are coupled with matter) and the higher-density matter of the shock wave. They test three different density cutoffs to define the shock wave, giving a range of potential estimates of the impact.
Given their model, the researchers simulate the deaths of nearly 200 progenitor stars, ranging in mass from nine times that of the Sun all the way up to 120 times.
Oh, the details…
In general, Gogilashvili and Tamborra find that flavor oscillations result in more energy being distributed into the higher-mass (meaning non-electron) neutrinos. And that means less energy gets transferred into the area of the shock, in some cases allowing it to stall, and thereby stopping the explosion. This is especially common on the lower end of the mass range they tested, where stars have around 15–30 solar masses; that also happens to overlap with the masses of red supergiants, potentially explaining why they seem to be blowing up less than they should.
