A magnetic field is a physical field that arises from an electric charge in motion, producing a force on another moving electric charge. Magnetic fields play a major role in star and planet formation, as well as at most stages of planetary system evolution.
Magnetic fields are present everywhere in the Universe, with intensities ranging from a fraction of a micro-Gauss (10−6 G) in the intergalactic medium to about 1 G for the Earth’s magnetic field and up to several peta-Gauss (1015G) in some highly magnetized compact objects, such as neutron stars. They play an important role in most physical processes at work in the Universe and are believed to be responsible for some spectacular behaviors, such as energetic collimated jets escaping from galactic nuclei or from protostars and young stars. They also constitute an essential ingredient of star and planet formation and their subsequent evolution. The Earth’s magnetic field has...