A team of scientists led by the Max Planck Institute for Astrophysics (MPA) has produced the highest resolution map of the Milky Way's magnetic field ever produced. The map pools over 41,000 measurements from across 26 projects. "The resulting database is equivalent to peppering the entire sky with sources separated by an angular distance of two full moons," said Dr. Tracy Clarke of the Naval Research Laboratory.
Each of the maps 41,330 individual data points represents a measurement of Faraday depth, a value of magnetic field strength along a particular line of sight. Polarized light from radio sources in space is observed for the Faraday effect, which describes the rotation of the plane of polarization. The degree and direction of rotation are determined, and from this the magnetic field strength in a given direction is established.
Even with such a rich source of data, the creation of a whole-sky map was by no means straightforward. In fact, its creation required MPA experts to use the new discipline of information field theory (IFT). IFT borrows the mathematical tools of information theory for coping with uncertainty, and adapts them to fields of data in three dimensional space. The scientists developed an algorithm known as the "extended critical filter" to cope with uncertainty and inaccuracies in the data.
The algorithm was employed with especial vigor when mapping the southern sky, for which data was comparatively lacking. Researchers were forced to interpolate between the data points available. The problem was compounded by the fact that accuracy varies between measurements, and no individual measurement (even the most accurate) is necessarily dependable in isolation. Further, due to the complexity of measuring processes, small errors have been found to significantly affect data.
In the new map, red areas indicate the parts of the sky where the magnetic field points towards the observer, while the blue areas indicate the opposite. At the midst of the map is the center of the galaxy.
It is hoped that the MPA's data and techniques will soon be used for the study of magnetic fields beyond the Milky Way, and that next generation radio telescopes will further enrich the map of our galaxy's magnetic field and perhaps help us unlock the secret of its origin.
Source: Naval Research Laboratory