Radio waves from a distant pulsar travel through the interstellar medium, encountering invisible magnetic structures the size of the distance from the Sun to Earth. One such structure is a current sheet, where the magnetic field abruptly changes direction, like a compass needle flipping from north to south. Until recently, directly observing such a flip was impossible: standard methods average the signal over the entire path spanning hundreds of light-years, and the fine detail drowns in the overall background.

But pulsars have a quirk: their radio signal scintillates, like the light of a distant star through turbulent atmosphere. Astronomers have learned to reconstruct the waveform from this scintillation with phase accuracy — the position of the oscillation within its cycle. By comparing the phases of the two polarizations (left and right circular), one can extract the difference in rotation measures — a quantity indicating how much the magnetic field has rotated the plane of polarization. This is precisely the technique applied to archival observations of pulsar B0834+06, made in 2005 with the Arecibo and Green Bank telescopes.

The data revealed a "1-millisecond lens"—a plasma structure causing a signal delay of one thousandth of a second. It turned out to split into two branches, whose angular separation decreases with frequency as ν⁻², consistent with scintillation theory. For six low-frequency sub-bands (311.5–321.5 MHz), the rotation measure difference between the branches was measured: Δ(ΔRM) = (−9.3 ± 3.2) × 10⁻³ rad/m². This is a 2.9σ signal — not yet a discovery, but a serious claim.

Translating the measured difference into a corrugated current sheet model, the authors obtained a magnetic field jump of |Δ⟨B∥⟩| ≈ 4.4 ± 2.1 μG. This value agrees with estimates for the warm ionized medium, where thermal and magnetic energies are roughly equal. Thus, the structure is not a random fluctuation but a long-lived element of interstellar turbulence.

Previously, it was unknown whether current sheets with field reversals exist on such scales. Now it has been shown that the pulsar scintillation method with phase retrieval can detect them. This is the first, albeit marginal, signal of a magnetic reversal in the interstellar medium. If the method is scaled to other pulsars, one could map magnetic fields on small scales and refine how cosmic rays wander through the galaxy. This, in turn, could aid in the search for the gravitational wave background via pulsar timing irregularities.