Nature of the inner ridge and helical jet structure

Determine whether the inner ridge and helical structure of the M87 jet arise from genuine physical jet substructure, Kelvin–Helmholtz instabilities, or imaging artefacts.

Background

The paper discusses a transverse triple-ridge structure in the M87 jet and notes that simulations have shown that a central filament in edge-brightened models can be produced by CLEAN imaging artefacts. A marginal detection with regularized maximum-likelihood imaging provides some independent evidence, but does not resolve the issue.

Consequently, the physical nature of the inner ridge and the broader helical jet structure remains unresolved.

References

However, the physical origin of such structures remains uncertain.

— A Helical Trajectory Interpretation of a Multi-wavelength Event in a Blazar S5 0716+714  (2609.30053 - Ouyang et al., 24 Sep 2026) in Section 5.2, “Locating the inferred helical trajectory and its possible magnetic interpretation”

However, it remains challenging to distinguish between these two scenarios based solely on current observations.

— A Helical Trajectory Interpretation of a Multi-wavelength Event in a Blazar S5 0716+714  (2609.30053 - Ouyang et al., 24 Sep 2026) in Section 5.2, “Locating the inferred helical trajectory and its possible magnetic interpretation”

The nature of this inner ridge and helical jet structure remains an open question.

— RadioAstron space-VLBI imaging of the jet in M87: II. The parsec-scale structure at 4.8 GHz  (2609.18192 - Kravchenko et al., 16 Sep 2026) in Introduction, paragraph discussing the VSOP and RadioAstron jet structure

A detailed simulation is needed to address the question of whether this upstream optically thin emission might represent the substructure of the core.

— RadioAstron space-VLBI imaging of the jet in M87: II. The parsec-scale structure at 4.8 GHz  (2609.18192 - Kravchenko et al., 16 Sep 2026) in Section 4.2, “Spectra”