We study the interaction of planetary nebulae with a magnetized interstellar medium (ISM) and show that the ISM magnetic field cannot be ignored in analysis of the interaction of planetary nebulae with (PNs) with the ISM. We show that stretching and bending of magnetic field lines can increase the effective pressure of the ISM. In particular, near the stagnation point of the flow of the ISM around the nebula, the ISM magnetic pressure can overcome the thermal pressure, leading to strong MHD instabilities even in isothermal flows. At early stages, when the planetary nebula outer regions are still neutral, the ISM magnetic field can penetrate the nebula via ambipolar diffusion. As a result, when pulled downstream by the flow, the magnetic field will strip the outer layers of the nebula. The RayleighTaylor and Kelvin-Helmholtz instabilities with wavenumbers along the magnetic field lines are suppressed. Therefore, the ISM magnetic field can break the cylindrical symmetrical nature of the interaction.
- ISM: magnetic fields
- Planetary nebulae: general