Planck telescope records light reflecting off interstellar dust grains
ESA and the Planck Collaboration
If the Milky Way were one giant magnet, sprinkling iron filings around it would trace the galaxy’s magnetic field. Scientists have found a more practical way to map the field using the Planck telescope.
To do so, Planck measured the polarization of microwave light that permeates space. When light is polarized, its electric fields all point in the same direction. Light reflecting off interstellar dust grains becomes polarized in the direction the grains are aligned; that direction, in turn, is steered by the galaxy’s magnetic field.
Planck’s map, reported in four papers posted May 5 at ArXiv.org, shows the entire sky with a dark band through the center representing the plane of the galaxy. Darker shading reflects more-polarized light. The lines mark the direction of the magnetic field.
The galactic magnetic field is about 100 million times as weak as a refrigerator magnet, and yet it may be crucial to the formation of stars. The field map is also