Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21812908w&link_type=abstract
American Astronomical Society, AAS Meeting #218, #129.08; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Parker instability arises from the presence of magnetic fields in a plasma in a gravitational field such as the interstellar medium (ISM), wherein the magnetic buoyant pressure expels the gas and causes the gas to move along the field lines. The subsequent gravitational collapse of the plasma gas is thought to be responsible for the formation of giant molecular clouds in the Galaxy. The process of mixing in the ISM near the Galactic plane is investigated. The initial ISM is assumed to consist of two fluids: plasma gas and cosmic-ray particles, in hydrostatic equilibrium, coupled with a uniform, azimuthally-aligned magnetic field. After a small perturbation, the unstable gas aggregates at the bottom of the magnetic loops and forms dense blobs. The growth rate of the instability decreases as the coupling between the cosmic rays and the plama becomes stronger (meaning a smaller cosmic-ray diffusion coefficient). The mixing is enhanced by the cosmic-ray diffusion, while the shape of the condensed gas depends sensitively on the initial equilibrium conditions. The perpendicular or cross field lines diffusion coefficient kappa_cross is often substantially smaller than the parallel coefficient kappa_0, only around 2%-4% of kappa_0. However, even with the minimum cross field diffusion, the mixing is significantly enhanced. The galactic wind flow perpendicular to the galactic disk may be greatly facilitated by Parker instabilities through the cross field diffusion of cosmic rays.
Ko Changhyun
Lo Ying-Yi
Wang Chih-Yueh
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