Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983sciam.249...44p&link_type=abstract
Scientific American (ISSN 0036-8733), vol. 249, Aug. 1983, p. 44-54.
Astronomy and Astrophysics
Astronomy
7
Cosmology, Dynamo Theory, Interstellar Magnetic Fields, Magnetic Fields, Planetary Magnetic Fields, Solar Magnetic Field, Astronomical Models, Galactic Rotation, Geomagnetism, Magnetic Anomalies, Magnetohydrodynamic Flow, Planetary Rotation, Stellar Rotation
Scientific paper
Descriptive models for the dynamo processes that generate magnetic fields around celestial objects are reviewed. Magnetic fields are produced, along with an electric current, when a conductor is moved perpendicularly through a magnetic field, so long as the resulting current is fed back into the conductor to amplify the current and field. In MHD theory, the lines of force of the magnetic field travel with the conducting fluid. A weak current or field must be present initially to generate the field. Planets have molten cores and stars have ionized gases to act as the conductors, and all space has sufficient gas with free electrons. The rotations of the planets, stars, and galaxy enhance the magnetic fields. Convective patterns have been characterized in the earth's molten core because of anomalies observed in the magnetic field at the surface. It has been shown that the faster a planet rotates, the more powerful its magnetic field is. However, fluid motions will produce fields only if the fluid motion is helical. The exact mechanism in stars could be primordial magnetism trapped during formation. However, in galaxies, the Biermann battery effect, wherein free electrons move along the surfaces of stars, could create enough of a field for the amplification process to proceed.
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