Experience indicates that most of the matter in the Universe is
composed of ionized or partially ionized gas permeated by
magnetic fields. Celestial objects are magnetized and magnetic
fields of significant strength are found everywhere in the
interstellar space, and over small and very large scales, in the
extragalactic universe. In general, small compact objects have
the largest magnetic field strengths, while larger low-density
objects have weaker magnetic fields. The Earth has a bipolar
field of about 0.5 G at its surface, originating from an
idealized current due to the charged fluid motion going
circularly in a ring inside the liquid molten metallic core. On
the Jupiter surface the magnetic field is about 4 G, owing to
the fast Jupiter rotation. In the interplanetary space of the
solar system the magnetic fields are of the order of 50 µG. On
the Sun, the magnetic field is of 10 G at the poles, while
localized sunspots on the surface near the equatorial zone of
the Sun, and more generally of a star, can