About the MKSP
Motivation: Cosmic Magnetic Fields
Magnetic fields are present in almost every place in the Universe. Most of the luminous matter is tightly coupled to magnetic fields. Large-scale fields intersperse the gas in the Milky Way,in galaxies and in galaxy clusters. They contribute to the nonlinear interplay of turbulent motions in the interstellar and intracluster medium. The magnetic energy content affects the evolution of galaxies and galaxy clusters, contributes significantly to the total pressure of interstellar gas, is essential for the onset of star formation, and controls the density and distribution of cosmic rays in the interstellar medium (ISM). In spite of their importance, the evolution, structure and origin of magnetic fields are still open problems in fundamental physics and astrophysics.
Most of what we know about astrophysical magnetic fields has been detected via radio astronomical observations. Most of the cosmic broad-band (“continuum”) radio emission is synchrotron radiation by relativistic electrons which spiral around magnetic field lines. In galaxies, these electrons are probably accelerated in the remnants of supernova explosions, together with other particles of the cosmic ray population. On larger scales, they may be accelerated by shocks, or turbulence, although these are also open questions.
Whatever their origins, magnetic fields are compressed, amplified and distorted by dynamo processes driven by turbulent gas motions, by cosmic rays, and by various feedback mechanisms. The observed synchrotron luminosity allows us to measure the total field strength. Synchrotron radiation is linearly polarized, up to 75% in a fully ordered magnetic field. The polarization plane yields the orientation of the regular field in the plane of the sky. The degree of linear polarization tells us the field’s degree of ordering. Moreover, Faraday rotation of the polarization plane provides information on the strength and direction of the field component along the line of sight. Hence, a three-dimensional picture of cosmic magnetic fields can be derived from radio waves.