Tracing Magnetic Fields with Aligned Grains

By A. Lazarian. 2007

343 citations recorded by the source corpus.

Magnetic fields play a crucial role in various astrophysical processes, including star formation, accretion of matter, transport processes (e.g., transport of heat), and cosmic rays. One of the easiest ways to determine the magnetic field direction is via polarization of radiation resulting from extinction or/and emission by aligned dust grains. Reliability of interpretation of the polarization maps in terms of magnetic fields depends on how well we understand the grain-alignment theory. Explaining what makes grains aligned has been one of the big issues of the modern astronomy. Numerous exciting physical effects have been discovered in the course of research undertaken in this field. As both the theory and observations matured, it became clear that the grain-alignment phenomenon is inherent not only in diffuse interstellar medium or molecular clouds but also is a generic property of the dust in circumstellar regions, interplanetary space and cometary comae. Currently the grain-alignment theory is a predictive one, and its results nicely match observations. Among its predictions is a subtle phenomenon of radiative torques. This phenomenon, after having stayed in oblivion for many years after its discovery, is currently viewed as the most powerful means of alignment. In this article, I shall review the basic physical processes involved in grain alignment, and the currently known mechanisms of alignment. I shall also discuss possible niches for different alignment mechanisms. I shall dwell on the importance of the concept of grain helicity for understanding of many properties of grain alignment, and shall demonstrate that rather arbitrarily shaped grains exhibit helicity when they interact with gaseous and radiative flows.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/5c4878f5d6fa44355bd0eb447bfcffdf77f78250

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Citations in the corpus

Radiative torques: analytical model and basic properties (2007, methodology): “The difference of our phase maps from those in DW97 is that here we present the alignment in respect 9 In Hoang & Lazarian (2007), we will show that zero angular momentum attractor points become attractor points at thermal angular momentum due to thermal wobbling c© 0000 RAS, MNRAS 000, 000–000 to…”
THE LEGACY OF SCUPOL: 850 μm IMAGING POLARIMETRY FROM 1997 TO 2005 (2009, background): “The degree of polarization is in essence a measure of how effectively the grains have been aligned (see Lazarian 2007 and references therein).”
The Efficiency of Grain Alignment in Dense Interstellar Clouds: a Reassessment of Constraints from Near-Infrared Polarization (2007, methodology): “This criterion is based on calculations in Hoang & Lazarian (2007), who studied the influence of gas bombardment on alignment by radiative torques using the Langevin equation approach: it was shown that when grains are aligned by radiative torques at an attractor point with an angular momentum…”
Radiative torque alignment: essential physical processes (2007, background): “We briefly described this in Lazarian (2007) and Lazarian & Hoang (2007a).”
The pre-launch Planck Sky Model: a model of sky emission at submillimetre to centimetre wavelengths (2012, background): “Polarisation of starlight by dust grains indicates partial alignment of elongated grains with the Galactic magnetic field (see Lazarian 2007, for a review of possible alignment mechanisms).”
TADPOL: A 1.3 mm SURVEY OF DUST POLARIZATION IN STAR-FORMING CORES AND REGIONS (2013, background): “Under most circumstances, spinning dust grains align themselves with their long axes perpendicular to the Bfield (e.g., Hildebrand 1988; Lazarian 2003, 2007; Hoang & Lazarian 2009; Andersson 2012), so the thermal radiation from these grains is polarized perpendicular to the B-field.”
Studies of Regular and Random Magnetic Fields in the ISM: Statistics of Polarization Vectors and the Chandrasekhar-Fermi Technique (2008, methodology): “This fact opens new horizons for polarimetric studies of magnetic fields (Yan & Lazarian 2006, 2007, 2008).”
Three-Dimensional Dust Radiative Transfer ∗ (2013, background): “Although alignment of grains has been demonstrated observationally for many decades, the physical mechanism for grain alignment is still a matter of debate (Lazarian 2007).”
Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust (2014, background): “While the details of this process remain unclear (Lazarian 2003, 2007), there is a consensus that the angular momentum of a grain spun up by photon-grain interactions (Dolginov & Mitrofanov 1976; Draine & Weingartner 1996, 1997; Lazarian & Hoang 2007; Hoang & Lazarian 2008) becomes aligned with the…”