Imagine a packed dance floor where dancers glide without any friction — passing through each other without a touch. That's a superfluid. In a neutron star's crust, neutrons could behave this way, but a rigid lattice of ions gets in the way, like suddenly sticking the dance floor full of pillars. It was commonly thought that the lattice stands still, and superfluidity almost vanishes.
However, the authors found that the pillars don't stay put. Quantum nature makes the ions jitter around their equilibrium: this is called zero-point motion (a trembling that persists even at absolute zero temperature). This jitter slightly blurs the obstacles, giving neutrons a chance to seep through the lattice. The scientists ran three-dimensional calculations for two types of ion packing, face-centered cubic and body-centered cubic, and in both cases, the superfluid fraction of neutrons remained strongly suppressed in the middle part of the crust. But not down to zero.
This dance with obstacles matters for the star's life. Superfluidity affects how fast a neutron star slows its rotation and how its crust cools. If the lattice isn't perfectly rigid, heat escapes differently, and glitches in the rotation period may occur in a different way. So atomic jitter on picometer scales rewrites the fate of an object the size of a city.
The zero-point vibrations of ions in a neutron star's crust have energies comparable to thermal energies at millions of degrees, yet they exist even at temperatures a billion times lower.
In Robert Forward's novel Dragon's Egg, life on the surface of a neutron star is depicted, where superfluidity and quantum effects become part of everyday reality.