Heliopause instability and its possible relation to soft X-ray emission

The heliopause (HP) is a tangential discontinuity that divides the interacting solar wind (SW) and local interstellar medium (LISM) flows. It is known, both from numerical calculations and linear stability analysis, that charge exchange between neutral and plasma particles can result in violent instability of the HP nose. This instability is of Rayleigh-Taylor type, the role of gravitation being played by momentum transfer between neutral and charged components of partially ionized plasma. Although secondary neutral particles originating in the inner heliosheath do decrease the intensity of instability, our multi-fluid calculations performed with the application of adaptive mesh refinement technique show that it still results in violent oscillations of the heliopause. Besides, low numerical dissipation allowed us to demonstrate that the HP flanks are also Kelvin-Helmholtz unstable. The important discovery is that the presence of secondary neutrals is essential for producing substantial instability of this kind. We analyze the amplitudes of the HP and termination shock (TS) oscillations and the speed of their global motion. The HP may be one of the regions contributing to soft X-ray emission. This is because of charge exchange of multiply ionized heavy ions with neutral atoms. It is possible that mixing of the LISM and SW plasmas can enhance the intensity of this emission. We calculate the X-ray intensity by integrating the production rate along different lines of sight in order to analyze this possibility.