MHD flows at astropauses and in astrotails

TL;DR

This paper models magnetohydrodynamic flows at astropauses and in astrotails, revealing complex magnetic null points and structures that influence cosmic ray acceleration and the shape of stellar wind interaction regions.

Contribution

It provides a detailed classification of counter-flow configurations and calculates electromagnetic fields to understand large-scale dynamics and particle acceleration mechanisms.

Findings

Multiple magnetic null points and separatrices exist in the interaction regions.

Extended tail structures naturally form and influence particle acceleration.

Complex magnetic topologies impact the shape of astropauses and astrotails.

Abstract

The geometrical shapes and the physical properties of stellar wind -- interstellar medium interaction regions form an important stage for studying stellar winds and their embedded magnetic fields as well as cosmic ray modulation. Our goal is to provide a proper representation and classification of counter-flow configurations and counter-flow interfaces in the frame of fluid theory. In addition we calculate flows and large-scale electromagnetic fields based on which the large-scale dynamics and its role as possible background for particle acceleration, e.g. in the form of anomalous cosmic rays, can be studied. We find that for the definition of the boundaries, which are determining the astropause shape, the number and location of magnetic null points and stagnation points is essential. Multiple separatrices can exist, forming a highly complex environment for the interstellar and stellar plasma. Furthermore, the formation of extended tail structures occur naturally, and their stretched field and streamlines provide surroundings and mechanisms for the acceleration of particles by field-aligned electric fields.