A neutron star the size of a city is the compressed core of a dead star. Some become pulsars — cosmic lighthouses with periodic flashes. Their magnetic field is billions of times stronger than Earth's; at the poles it bursts out like a violent fountain. There, myriads of axions are born — invisible particles that could be dark matter.

The axion field resembles an intangible fluid. As light pushes through, its oscillations twist slightly — like a boat changing course in an imperceptible current. Measuring this angle can reveal the axion's properties, though near a neutron star the usual picture breaks down.

But the main surprise is the vortices. At the poles, plasma washes out axions, leaving microscopic voids. They collapse in billionths of a second, a process detectable by ultra-precise atomic clocks. So to catch elusive dark matter, you don't need giant underground detectors — you can simply observe the rhythm of emptiness near a neutron star.