The Sun moves through the interstellar medium, and the solar wind — a supersonic outflow of charged particles — inflates a bubble called the heliosphere. Behind the Sun (relative to its motion), the heliosphere stretches into a tail, like a comet but at stellar scale. The tail's structure has been debated: is it a single stream, a split pair of lobes, or something more complex?
Kornbleuth et al. (arXiv:2603.13088) analyze high-energy energetic neutral atoms (ENAs) detected by IBEX and find signatures of a split heliospheric tail with magnetic reconnection occurring between the lobes. The tail isn't a smooth wake — it's bifurcated, with the solar magnetic field's polarity flipping between the northern and southern lobes, and reconnection happening at the interface where the two polarities meet.
ENAs are produced when fast ions from the solar wind exchange charges with slow interstellar neutral atoms. The resulting neutral particles travel in straight lines (unaffected by magnetic fields) back to Earth's orbit, carrying information about conditions at the point of exchange. By mapping ENA energies and directions, you reconstruct the 3D structure of the heliosphere's outer boundary.
The split-tail signature appears as an ENA depletion along the heliospheric equator — the region between the two magnetic lobes where reconnection converts the organized flow into heated, isotropic plasma that produces fewer ENAs at the observed energies. The dip in the ENA map is the shadow of reconnection.
This transforms the heliospheric tail from a passive wake into an active site of magnetic energy dissipation. The solar magnetic field, stretched and compressed by the solar wind's interaction with the interstellar medium, finds its release not at the nose of the heliosphere (where the wind shocks against the medium) but in the tail, where oppositely directed field lines annihilate. The tail is where the Sun's magnetic energy is finally spent.