Ever since neutron stars were discovered, researchers have been using their unusual properties to probe our universe. The superdense remnants of stellar explosions, neutron stars pack a mass greater than the Sun’s into a ball about as wide as San Francisco. A single cup of this star matter would weigh about as much as Mount Everest.

Both cold gases and neutron matter in some parts of a neutron star are superfluids – the particles flow without any friction. When a superfluid rotates, little whirlpools, or vortices, develop. How exactly these vortices move and interact with one another and other structures inside a rotating neutron star is still an open question. “It’s probably not this nice, regular lattice of vortices,” says Michael McNeil Forbes, who studies theoretical physics at Washington State University in Pullman. “It might be some tangle of vortices that’s in the entire star. We don’t know.”

Forbes and others suspect that the glitches they observe in the rotation of pulsars have something to do with how these vortices get “pinned” to structures in the star. Generally, a single vortex meanders freely around a fluid. But when the fluid contains a rigidly packed area of matter that obstructs the vortex’s motion, the vortex will stop and sometimes even wrap its swirling arms around the rigid object and position itself so that its centre is right on top of it.

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