A sudden jump in a stellar clock
The Vela pulsar is a rapidly rotating neutron star whose radio beams sweep past Earth like a lighthouse. By timing those pulses, astronomers can track its rotation with extraordinary precision. During a glitch, the pulses arrive slightly sooner than expected: the star’s visible outer layers have abruptly begun spinning faster.
The jump is small in everyday terms, but it happens across an object only a few dozen kilometers wide and packed to densities far beyond anything on Earth. The key is that the solid crust is not the star’s only rotating component.
A hidden reservoir of angular momentum
Below the crust, some neutrons form a superfluid—a state of matter that flows without ordinary friction. It does not simply rotate as a smooth liquid. Its rotation is carried by tiny whirlpools called vortices, which can become pinned within the crust’s irregular structure. While pinned, the superfluid can keep rotating at a different rate from the solid outer layers, storing angular momentum like a flywheel held back from turning freely.
If vortices break loose and move outward, the superfluid’s rotation slows. The crust and the rest of the star then gain some of its angular momentum and speed up together. That transfer is the leading explanation for the abrupt spin-up seen in pulsar glitches.
Where a starquake fits
The crust is under immense stress, and it may crack or shift as the star’s shape and rotation change. Such a starquake could help disturb pinned vortices and trigger a glitch. But a fracture is not required by the basic explanation, and the precise trigger is still uncertain; the well-supported picture is an exchange of angular momentum between the superfluid interior and the crust.
So the hard-boiled-egg comparison captures the sudden change in spin, but not a literal collision between the whole core and shell. A glitch is a brief release of motion stored inside a star—and its pulse timing lets astronomers watch that hidden interior affect the star’s clock.
