Axions at the Poles: Key to Dark Matter express
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.
Original abstract
as written by the authors arXiv:2603.28826
Recent investigations by Noordhuis et al. [1, 2] and others have demonstrated the occurrence of strong local inhomogeneous axion regions in the polar cap regions of neutron stars. These regions are characterized by static magnetic fields $$B_0 \sim 10^8\,$$T ($$=10^{12}\,$$G) directed normally outwards from the polar surface (magnetic dipole), together with static electric fields $$E_0 \sim 10^{-6}cB_0$$ in the same direction (electric dipole). An enormous increase of axion production, up to order $$10^{50}$$, is predicted in the polar regions. These features are important for phenomena such as polarization plane rotation under both weak and strong axion field populations. We survey the peculiar antenna property of conductive materials, which shows the need for having very strong magnetic fields to make the detection possible. We present the general form of electromagnetic waves in the axion environment, in both the standard form and in a physically instructive hybrid one, showing the nonreciprocity of axion fluid, and calculate the polarization rotation. The rotation is well defined in the case of weak, but still stronger than average value of axion fields in Universe. For very strong fields such a perturbative theory breaks down, however. A noteworthy general property of the rotation of polarization plane is that it can only occur when the axion cloud is varying in space or time. We limit ourselves only variation in space. Finally, as application we discuss the physical picture of local 'gap' regions proposed by Noordhuis et al. in the polar regions of a neutron star. The reason for occurrence of these gaps is plasma effects. To evaluate the time scales involved, we calculate the filling time for surrounding axions flowing into an initial gap. It turns out that the typical filling time is a moderate number of nanoseconds, within the accuracy of atomic clocks precision to be detectable.
A neutron star's magnetic field can rip an ordinary magnet to atoms, and in its crust, atomic nuclei are packed so densely that a teaspoon of matter would weigh billions of tons.