Richard Wielebinski

Talk title

Cosmic Magnetic Fields

Abstract

Magnetic fields have been observed in nearly all cosmic objects. The magnetic field of the Earth has been known since antiquity, while the Sun was shown to have considerable magnetic fields in sunspots by Zeeman effect measurements. Details of solar magnetic fields in the corona are seen during eclipses and are observable by satellites. In the solar system we have in-situ measurements made by satellites. Optical polarimetry gave us the first hints about the presence of magnetic fields in the Milky Way and later in nearby galaxies. Radio astronomy gave us several methods of observing magnetic fields. The non-thermal radio continuum, which is polarized synchrotron emission, is a tracer of magnetic fields. Faraday effects are observed in the radio domain giving us additional information about the passage of polarized radio waves through thermal regions with magnetic fields. Also the Zeeman effect has been used at radio wavelength to measure magnetic fields in molecular clouds. Magnetic fields are present in supernova remnants, in pulsars, in star forming regions, etc. Large scale magnetic fields, as well as smaller scale structures, have been observed in nearby galaxies. Magnetic fields are present in very distant galaxies since their radio emission is non-thermal and hence due to the synchrotron process. In clusters of galaxies magnetic fields have been detected in the intergalactic space. In my talk, I will describe the present status of our knowledge about magnetic fields in cosmic objects and will summarise the situation with the interpretation of magnetic phenomena.