When a massive star dies, its core collapses, and a neutrino storm is born. These ghostly particles fly outward, changing their flavor along the way, like a chameleon changes color. This dance of flavors can either boost the explosion or, conversely, dampen it.
But this dance has a choreographer — the density gradients of matter. Scientists built a global model in spherical symmetry and saw that if the density changes too abruptly, the dance freezes. Particles don't have time to adjust, just as a runner can't make a sharp turn at full speed.
The big surprise is the artificial damping of oscillations. It's added to calculations for simplicity, but it smears the picture: the suppression of transformations appears stronger than it really is. The authors derived a simple formula that will help build more honest models of supernovae and neutron star mergers.
So next time you look at the night sky, remember: somewhere out there, in the fiery heart of a dying star, ghostly particles are deciding the fate of the explosion.
Neutrinos are so ubiquitous that trillions of these particles, born in distant stars, pass through your body every second.