Fluid Dynamical Instabilities in a Partially Ionized Flow

Details Fluid Dynamical Instabilities in a Partially Ionized Flow Fluid Dynamical Instabilities in a Partially Ionized Flow

May 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...534..309k&link_type=abstract

The Astrophysical Journal, Volume 534, Issue 1, pp. 309-316.

Astronomy and Astrophysics

Astronomy

3

Diffusion, Instabilities, Ism: Magnetic Fields, Magnetohydrodynamics: Mhd, Stars: Formation

Scientific paper

In this paper, we reveal that there are two fluid dynamical instabilities for a partially ionized flow with quasi-static contraction: the instability of the Alfvén wave and the two-fluid instability. We find them by means of linear perturbation analysis, adopting the following unperturbed state; the magnetic field has a gradient against the terminal flow of neutrals, which are accelerated because of gravity. The terminal velocity is determined by the balance between the gravity and the friction force, which originates from the ion-neutral collisions. The instability of the Alfvén wave occurs because of the imbalance of the restoring force, which is generated by the unperturbed background magnetic field if a wavelength is longer than a critical wavelength. Indeed, this critical wavelength is obtained from the comparison between the local restoring efficiency and that of the background unperturbed field. It is estimated as of the order of ~0.01 pc when the grains are the dominant charged particles. Thus, we speculate that this instability is responsible for the formation of the observed small-scale structure in the molecular clouds. If the relative speed between the ions and the neutrals is larger than the thermal speed of the neutrals, there is another instability, i.e., the so-called two-fluid instability. Fortunately, although the two-fluid instability coexists with the instability of the Alfvén wave, structure formation via the instability of the Alfvén wave is possible since its growth rate is larger than that of the two-fluid instability.

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