Kimihiro Nomura

A century ago, magnetic observatories recorded only the slow breathing of Earth's core. Today, their data have become hunting grounds for particle physics. At the Eskdalemuir Observatory in northern England, fluctuations of the magnetic field are recorded every hundredth of a second.

The nature of dark matter has been puzzling physicists for decades. Among the candidates, axions hold a special place — ultralight particles that could simultaneously solve the strong CP problem. If they exist, they barely interact with light, rotating its polarization plane.

In a close binary system, the hot star, like a searchlight, illuminates its cooler companion. Some of the light scatters off free electrons in its atmosphere — this is Thomson scattering — and acquires linear polarization. As the stars orbit each other, this polarization rotates, like the hand of a peculiar cosmic metronome.