The interstellar medium displays turbulence with a spectrum of electron density fluctuations whose scales extend from 1018 m to 106 m. Theoretical work within CMSO has shown that the density fluctuations are linked to magnetic field fluctuations at small scales (near 10⁶ m) and develop highly coherent, long-lived filament-like structures (seen end on as circular structures in the figures). The coupling is mediated by a kinetic-Alfvén-wave cascade that supplants the better-known shear-Alfvén-wave cascade when the turbulence approaches scales on the order of the ion gyration radius. The left hand figure shows contours of current and the right hand figure shows contours of density computed from a model for decaying kinetic Alfvén wave turbulence. The coherent structures produce non Gaussian probability density functions in both current and density. This work is significant because it provides a dynamical mechanism for non Gaussian density fluctuations, a condition inferred from the propagation of pulsar signals through the interstellar medium. The filaments are long-lived because strong magnetic shear from the filamentary current refracts turbulence away from the structures, thereby preventing their mixing by surrounding turbulence.

Reference: P.W. Terry and K. W. Smith, arXiv:astro-ph/0702177v1; submitted to ApJ.