Dynamo models for the structure of the regular magnetic field in the galaxy NGC 6946 are confronted with recent observations of polarized radio emission at λ3.5 cm. The observed behaviour of the concentration of regular fields between the gaseous spiral arms (“magnetic spiral arms”) is achieved via a non-axisymmetric azimuthal distribution of only the correlation time τcorr of interstellar turb...

The Parker instability, which has been considered as a process governing the structure of the interstellar medium, is induced by the buoyancy of magnetic field and cosmic rays. In previous studies, while the magnetic field has been fully incorporated in the context of isothermal magnetohydrodynamics, cosmic rays have been normally treated with the simplifying assumption of infinite diffusion al...

www.sciencemag.org SCIENCE VOL 326 13 NOVEMBER 2009 909 COVER The Interstellar Boundary Explorer (IBEX) spacecraft has returned the first global images of the interaction of our heliosphere with the local interstellar medium. IBEX observations show a ribbon of energetic neutral atoms (reds to greens), snaking between the positions of the two Voyager spacecraft (white dots). This ribbon marks th...

We examine MHD simulations of the propagation of a strong shock wave through the interstellar two-phase medium composed of small-scale cloudlets and diffuse warm neutral medium in two-dimensional geometry. The pre-shock two-phase medium is provided as a natural consequence of the thermal instability that is expected to be ubiquitous in the interstellar medium. We show that the shock-compressed ...

We follow numerically the nonlinear evolution of the Parker instability in the presence of phase transitions from a warm to a cold HI interstellar medium in two spatial dimensions. The nonlinear evolution of the system favors modes that allow the magnetic field lines to cross the galactic plane. Cold HI clouds form with typical masses ≃ 10 M⊙, mean densities ≃ 20 cm, mean magnetic field strengt...