Tracing Magnetic Field with Aligned Dust: Mystery Unveiled
Alex LAZARIAN
University of Wisconsin, Madison, USA
Résumé :
Aligned non-spherical dust particles both polarize
starlight passing through the dust cloud and emit polarized
far infrared and sub-mm radiation. This provides an easy way
to study magnetic fields in diffuse interstellar gas, hotbeds
of star formation, circumstellar regions and interplanetary
medium. The interpretation of the polarization in terms of
magnetic field, however, requires the knowledge
of the grain alignment theory. This has been the stumbling
block for reliable magnetic field tracing since 50s of
the previous century.
While great minds, e.g. Ed Purcell and Lyman Spitzer worked
productively in the field and contributed to it substantially,
I shall show that the textbook solutions of the problem
of grain alignment are not tenable for most of the interstellar
grains. Instead, I shall identify grain helicity, which stems
from their irregularity, as a most important component of
a successful grain alignment theory. I shall demonstrate a simple
analytical model of a helical grain that is able to explain the
existing observational data (including the cases when
the alignment fails) and thus allow more reliable studies
of magnetic fields. I shall discuss a few new condensed matter
effects, e.g. magneto-mechanical effects, which have been
discovered in the process of the grain alignment research.
