LONG-LIVED MAGNETIC-TENSION-DRIVEN MODES IN A MOLECULAR CLOUD

Journal Article · Thu Jun 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/716/1/427· OSTI ID:21450844

Basu, Shantanu

We calculate and analyze the longevity of magnetohydrodynamic (MHD) wave modes that occur in the plane of a magnetic thin sheet. Initial turbulent conditions applied to a magnetically subcritical cloud are shown to lead to relatively rapid energy decay if ambipolar diffusion is introduced at a level corresponding to partial ionization primarily by cosmic rays. However, in the flux-freezing limit, as may be applicable to photoionized molecular cloud envelopes, the turbulence persists at 'nonlinear' levels in comparison with the isothermal sound speed c {sub s}, with one-dimensional rms material motions in the range of {approx} 2 c {sub s}-5 c {sub s} for cloud sizes in the range of {approx} 2 pc-16 pc. These fluctuations persist indefinitely, maintaining a significant portion of the initial turbulent kinetic energy. We find the analytic explanation for these persistent fluctuations. They are magnetic-tension-driven modes associated with the interaction of the sheet with the external magnetic field. The phase speed of such modes is quite large, allowing residual motions to persist without dissipation in the flux-freezing limit, even as they are nonlinear with respect to the sound speed. We speculate that long-lived large-scale MHD modes such as these may provide the key to understanding observed supersonic motions in molecular clouds.

• OSTI ID: 21450844
• Journal Information: Astrophysical Journal, Vol. 716, Issue 1; Other Information: DOI: 10.1088/0004-637X/716/1/427; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
AMBIPOLAR DIFFUSION
COSMIC RADIATION
KINETIC ENERGY
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
NONLINEAR PROBLEMS
ONE-DIMENSIONAL CALCULATIONS
PHOTOIONIZATION
SOUND WAVES
STARS
DIFFUSION
ENERGY
FLUID MECHANICS
HYDRODYNAMICS
IONIZATION
IONIZING RADIATIONS
MECHANICS
RADIATIONS