Consequences of the heliopause instability caused by charge exchange

The heliopause (HP) is a tangential discontinuity that divides the interacting streams of the solar wind (SW) and local interstellar medium (LISM). It has been known for some time that the heliopause is subject to Rayleigh-Taylor instabilities driven and mediated by interstellar neutral atoms. Here we identify a new form of instability on the flanks of HP driven by hot neutral hydrogen atoms created by charge exchange of interstellar neutrals with hot heliosheath plasma. To investigate the instabilities and the consequences of these on heliospheric structure we performed high-resolution, shock-capturing, adaptive-mesh-refinement calculations of the SW-LISM interaction. Low numerical dissipation allows us to analyze the fine structure of the heliosheath resulting from the HP instability. We show that secondary neutrals play an essential role in destabilizing the flanks of the HP. We analyze the time-dependent location of the HP and the termination shock and the influence of their excursions on the plasma distribution in the inner heliosheath. It is found that perturbations generated by the HP instability can affect the distribution of plasma in the inner heliosheath on shorter timescales than the timescale of the instability as it develops near the stagnation axis. Finally, by way of application, we estimate the intensity of the soft X-ray emission generated in different regions of the HP and show that its instability leads to a substantial enhancement in the X-ray emission which bears an imprint of the HP shape.