Global identity of magnetopause and astropause

Determine whether the magnetic and hydrodynamic separatrices are identical globally when the magnetic and hydrodynamic fans are locally identical.

Background

The paper distinguishes local co-location of magnetic and velocity null points from the global equivalence of the surfaces generated by their field-line and streamline separatrices. Even if the tangential magnetic and hydrodynamic fans coincide in a neighborhood of the astropause apex, it remains unresolved whether the entire magnetic separatrix surface and hydrodynamic separatrix surface coincide throughout the global configuration. This question bears directly on whether the magnetopause and astropause are physically the same boundary.

References

Even if the null points of flow and magnetic field are co-located, one open issue is whether the tangential magnetopause (magnetic fan) is identical to the tangential astropause (hydrodynamic fan). This requires further investigation. When the two fans are identical locally, the second issue is whether the two separatrices are also identical globally, that is, whether magnetopause and astropause are identical.

— The existence of null points of flow and magnetic fields as prerequisites for the presence of astropauses and their co-location  (2610.09933 - Nickeler et al., 7 Oct 2026) in Section 5, Discussion and conclusions (following the discussion of Hall MHD)