Grain Alignment by Ambipolar Diffusion in Molecular Clouds

1995 ◽  
Vol 453 ◽  
pp. 238 ◽  
Author(s):  
W. G. Roberge ◽  
S. Hanany ◽  
D. W. Messinger
Keyword(s):  
Molecular Clouds ◽  
Ambipolar Diffusion ◽  
Grain Alignment

scholarly journals Magnetic Fields in Molecular Clouds—Observation and Interpretation

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 41
Author(s):  
Hua-Bai Li
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Zeeman Effect ◽  
Ambipolar Diffusion ◽  
Grain Alignment ◽  
The Past ◽  
Turbulence Velocity ◽  
Cloud Cores ◽  
Dust Grain

The Zeeman effect and dust grain alignment are two major methods for probing magnetic fields (B-fields) in molecular clouds, largely motivated by the study of star formation, as the B-field may regulate gravitational contraction and channel turbulence velocity. This review summarizes our observations of B-fields over the past decade, along with our interpretation. Galactic B-fields anchor molecular clouds down to cloud cores with scales around 0.1 pc and densities of 104–5 H2/cc. Within the cores, turbulence can be slightly super-Alfvénic, while the bulk volumes of parental clouds are sub-Alfvénic. The consequences of these largely ordered cloud B-fields on fragmentation and star formation are observed. The above paradigm is very different from the generally accepted theory during the first decade of the century, when cloud turbulence was assumed to be highly super-Alfvénic. Thus, turbulence anisotropy and turbulence-induced ambipolar diffusion are also revisited.

AMBIPOLAR DIFFUSION AND TURBULENT MAGNETIC FIELDS IN MOLECULAR CLOUDS

2011 ◽  
Vol 26 (04) ◽  
pp. 235-249 ◽  
Author(s):  
MARTIN HOUDE ◽  
TALAYEH HEZAREH ◽  
HUA-BAI LI ◽  
THOMAS G. PHILLIPS
Keyword(s):  
Magnetic Fields ◽  
Molecular Clouds ◽  
Ambipolar Diffusion ◽  
Star Forming ◽  
Star Forming Regions ◽  
Spin Interactions ◽  
Line Narrowing ◽  
Weakly Ionized ◽  
Novel Method

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.

The Langevin Equation and Its Application to Grain Alignment in Molecular Clouds

1993 ◽  
Vol 418 ◽  
pp. 287 ◽  
Author(s):  
W. G. Roberge ◽  
T. A. Degraff ◽  
J. E. Flaherty
Keyword(s):  
Langevin Equation ◽  
Molecular Clouds ◽  
Grain Alignment

scholarly journals Probing the turbulent ambipolar diffusion scale in molecular clouds with spectroscopy

2013 ◽  
Vol 438 (1) ◽  
pp. 663-671 ◽  
Author(s):  
T. Hezareh ◽  
T. Csengeri ◽  
M. Houde ◽  
F. Herpin ◽  
S. Bontemps
Keyword(s):  
Molecular Clouds ◽  
Ambipolar Diffusion ◽  
Diffusion Scale
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