Linear Gravitational Instability of Filamentary and Sheetlike Molecular Clouds with Magnetic Fields

We review the introduction and development of a novel method for the characterization of magnetic fields in star-forming regions. The technique is based on the comparison of spectral line profiles from coexistent neutral and ion molecular species commonly detected in molecular clouds, sites of star formation. Unlike other methods used to study magnetic fields in the cold interstellar medium, this ion/neutral technique is not based on spin interactions with the field. Instead, it relies on and takes advantage of the strong cyclotron coupling between the ions and magnetic fields, thus exposing what is probably the clearest observational manifestation of magnetic fields in the cold, weakly ionized gas that characterizes the interior of molecular clouds. We will show how recent development and modeling of the ensuing ion line narrowing effect leads to a determination of the ambipolar diffusion scale involving the turbulent component of magnetic fields in star-forming regions, as well as the strength of the ordered component of the magnetic field.

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Magnetic fields in molecular clouds: Regulators of star formation

The Physics and Chemistry of Interstellar Molecular Clouds: mm and Sub-mm Observations in Astrophysics - Lecture Notes in Physics ◽

10.1007/bfb0119504 ◽

2008 ◽

pp. 297-312

Author(s):

Telemachos Ch. Mouschovias

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

Molecular Clouds

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CO and the Multiphase ISM

Symposium - International Astronomical Union ◽

10.1017/s0074180900234025 ◽

1997 ◽

Vol 170 ◽

pp. 25-32

Author(s):

Christopher F. Mckee

Keyword(s):

Mach Number ◽

Magnetic Fields ◽

Interstellar Medium ◽

Molecular Clouds ◽

Molecular Gas ◽

Wave Pressure ◽

Multiphase Structure ◽

Co Observations

CO observations indicate that molecular clouds have a complex multiphase structure, and this is compared with the multiphase structure of the diffuse interstellar medium. The trace ionization within the molecular gas is governed primarily by UV photoionization. Magnetic fields contribute a significantly larger fraction of the pressure in molecular clouds than in the diffuse interstellar medium. Observations suggest that the total Alfvén Mach number, mAtot, of the turbulence in the diffuse ISM exceeds unity; Zeeman observations are consistent with mAtot ≲ 1 in molecular clouds, but more data are needed to verify this. Most molecular clouds are self-gravitating, and they can be modeled as multi-pressure polytropes with thermal, magnetic, and wave pressure. The pressure and density within self-gravitating clouds is regulated by the pressure in the surrounding diffuse ISM.

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Could bow-shaped magnetic morphologies surround filamentary molecular clouds?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936280 ◽

2019 ◽

Vol 632 ◽

pp. A68 ◽

Cited By ~ 3

Author(s):

M. Tahani ◽

R. Plume ◽

J. C. Brown ◽

J. D. Soler ◽

J. Kainulainen

Keyword(s):

Magnetic Field ◽

Monte Carlo ◽

Magnetic Fields ◽

Faraday Rotation ◽

Molecular Clouds ◽

Monte Carlo Analysis ◽

Line Of Sight ◽

Field Reversal ◽

Filamentary Structure ◽

Western Side

Context. A new method based on Faraday rotation measurements recently found the line-of-sight component of magnetic fields in Orion-A and showed that their direction changes from the eastern side of this filamentary structure to its western side. Three possible magnetic field morphologies that can explain this reversal across the Orion-A region are toroidal, helical, and bow-shaped morphologies. Aims. In this paper, we constructed simple models to represent these three morphologies and compared them with the available observational data to find the most probable morphology(ies). Methods. We compared the observations with the models and used probability values and a Monte Carlo analysis to determine the most likely magnetic field morphology among these three morphologies. Results. We found that the bow morphology had the highest probability values, and that our Monte-Carlo analysis suggested that the bow morphology was more likely. Conclusions. We suggest that the bow morphology is the most likely and the most natural of the three morphologies that could explain a magnetic field reversal across the Orion-A filamentary structure (i.e., bow, helical and toroidal morphologies).

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Turbulence and magnetic fields in molecular clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900239430 ◽

1991 ◽

Vol 147 ◽

pp. 83-92

Author(s):

R. N. Henriksen

Keyword(s):

Magnetic Fields ◽

Wavelet Analysis ◽

Molecular Clouds ◽

Fractal Structure ◽

Compressible Turbulence ◽

Dynamo Theory ◽

First Results ◽

Self Similar

in this paper I first review some of the simple structural concepts associated with compressible turbulence. In particular the hierarchical or self-similar fractal structure to be expected is formulated in a manner readily compared to the observations, and to previous work. In the next section I present the first results of a wavelet analysis on molecular clouds, which seem to comfirm the hierarchical scaling. I conclude with an extention of the theory to include magnetic fields. This latter theory represents an alternative to the more conventional dynamo theory.

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