Magnetic fields in the diffuse interstellar medium on scales of an astronomical unit (AU) are virtually uncharacterized. The classical picture of magnetohydrodynamic turbulence predicts an energy cascade from large to small scales, but on AU scales the medium becomes intermittent, fragmenting into current sheets. These structures can deflect cosmic rays of gigaelectronvolt energies by large angles, contradicting standard diffusion models. However, traditional methods for measuring magnetic fields, such as Faraday rotation, average the signal along the entire line of sight over hundreds of parsecs and are insensitive to AU-scale structures. This work follows a line of research where pulsar scintillation has already proven its ability to probe plasma density on AU scales, but the magnetic configuration has remained inaccessible.
The method relies on pulsar scintillation—the interference of radio waves scattered by inhomogeneities in the interstellar plasma. For archival observations of pulsar B0834+06 from the Arecibo and Green Bank telescopes (2005), phase retrieval is applied using the θ–θ method followed by Gerchberg–Saxton iteration. This allows reconstruction of the complex wave field for left and right circular polarizations. A cross-conjugate wave field (CCWF) is then formed, whose phase is proportional to the phase difference between polarizations. To isolate the signal from the '1-ms lens'—the presumed current sheet—the phase is calibrated against the main scintillation arc (line of sight) in each of 16 subbands of 2 MHz. In six low-frequency subbands (311.5–321.5 MHz), the two branches of the lens are resolved, and the difference in their differential rotation measures is measured.
As a result of phase retrieval, the '1-ms feature' splits into two branches whose angular separation decreases with frequency as ν⁻², consistent with scintillation theory. For the six subbands where the branches are separated, the inter-branch differential rotation measure difference is measured as Δ(ΔRM) = (−9.3 ± 3.2) × 10⁻³ rad/m², corresponding to a significance of 2.9σ. Within the model of a rippled current sheet, this translates into a difference in the line-of-sight averaged magnetic field of |Δ⟨B∥⟩| ≈ 4.4 ± 2.1 μG. The obtained value is consistent with estimates for thermal and magnetic energies in the warm ionized medium (β ≈ 1), indicating the long-lived nature of the structure.
This work demonstrates for the first time the possibility of measuring magnetic fields on AU scales in the interstellar medium using pulsar scintillation. Unlike previous studies that were limited to electron density, here the magnetic configuration itself is extracted—the field flip across the current sheet. This opens the way to testing theoretical models of intermittency and current sheets, as well as assessing their influence on cosmic-ray propagation.
The method can be scaled to other pulsars and observing epochs. For confident detection, multiple epochs and lines of sight will be required, as well as broader low-frequency bands to lift the λ² degeneracy. Including all four Stokes parameters will allow control of polarization leakage and improve accuracy.
The results are important for models of cosmic-ray propagation, especially for the dominant population with energies of order GeV, whose gyroradii are comparable to AU. They may also help correct scattering delays in pulsar timing for gravitational-wave background detection.
Conduct new observations with high time and frequency resolution at several radio telescopes, including interferometric arrays, to search for similar '1-ms lenses'. Accumulate statistics across different pulsars and epochs to assess the prevalence and temporal stability of AU-scale magnetic flips.
This work is directly related to the unresolved problem of the nature of intermittency in interstellar turbulence and the formation of current sheets at dissipative scales. It also touches on the question of the contribution of small-scale magnetic structures to cosmic-ray diffusion, which remains open.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The study demonstrates a method for measuring magnetic fields on AU scales in the interstellar medium using pulsar scintillation. From archival data of pulsar B0834+06, the wave field was reconstructed for two polarizations, and the inter-branch difference in the differential rotation measure was obtained, corresponding to a magnetic field reversal of ~4.4 μG at the 2.9σ level.
Where its strength is
The key strength is that, for the first time, the magnetic configuration itself (the field reversal across the current sheet) has been extracted on AU scales, not just the plasma density. This opens the way to directly test models of intermittency and current sheets in the interstellar medium.
Where it could go next
Worth trying
Why this may matter
This method opens a new observational window into the physics of interstellar turbulence on scales where intermittency and current sheets dominate. Such measurements are critical for understanding cosmic-ray scattering and could influence models of diffusion in the Galaxy.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.57, against a usual 0.64. It looks like few have drilled nearby.
The size of the current sheet that was 'seen' is about 0.6 astronomical units — smaller than the distance from the Sun to Earth. Yet the pulsar itself is hundreds of parsecs away, meaning millions of times farther.
The idea that invisible magnetic structures in the interstellar medium can influence particle trajectories resembles the concept of 'gravitational lenses' from science fiction, but here the lensing is done by plasma and magnetic fields, not gravity.