Vol. 556
In section 2. Astrophysical processes

On the origin of non-self-gravitating filaments in the ISM

by P. Hennebelle, A&A 556, A153


Filaments are ubiquitous in the interstellar medium, as recently emphasized by Herschel observations, but their physical origin remains elusive. In this paper, the author uses ideal MHD simulations to study the formation of non-gravitating clumps in various conditions, including different setups, magnetization, and Mach numbers. On average, clumps in MHD simulations are more filamentary than clumps in hydrodynamic simulations. Detailed analyses reveal that the filaments are in general preferentially aligned with the strain, indicating that they simply result from the stretch induced by turbulence. Moreover, filaments tend to be confined by the Lorentz forces, which therefore lead them to survive longer in magnetized flows. The author concludes that filaments are ubiquitous because they are the results of the very generic turbulent strain, and because the magnetic field helps to keep them coherent. Energy dissipation appears to play a fundamental role in filament formation.