Impact of Supernovae on the Interstellar Medium and the Heliosphere

Abstract

The effect of supernovae on their environment is discussed in general and on the heliosphere in particular. It is shown that supernovae generate turbulence on scales of the order of 100 parsecs (pc), which leads to the formation of structures in the interstellar medium, e.g., filaments, down to the viscous scale. This so-called integral scale, at which turbulence is fed in, corresponds to the average size of supernova remnants (and superbubbles) at their breakup in an inhomogeneous medium. The characteristics of high Reynolds number compressible interstellar turbulence are discussed, as well as its implications for 3D numerical modeling. It is found that the average thermal pressure, P th , is in general lower than the frequently quoted value of P th ∕ k B ∼ 10, 000 ( k B being Boltzmann’s constant) due to the closure of a galactic fountain cycle, which releases pressure in the disk. Thermal cooling is out of equilibrium, as a rule, because delayed ionization and recombination can be important, making the a priori assumption of collisional ionization equilibrium used in many simulations questionable. The strong shocks, bounding the supernova remnants, are the sites of high-energy particle acceleration (cosmic rays), which fill, and diffuse through, the whole galactic disk, eventually entering the heliosphere, which originates from the interaction of the solar wind with the local interstellar medium. We describe the most important processes that govern the interstellar medium and the heliosphere and discuss their physical relationship.