Magnetic helicity in galactic dynamos

Abstract

Magnetic fields correlated on kiloparsec scales are seen in spiral galaxies. Their origin could be due to amplification of a small seed field by a turbulent galactic dynamo. We review the current status of the galactic dynamo, especially the constraints imposed by magnetic helicity conservation. We estimate the minimal strength of the large-scale magnetic field which could arise inspite of the helicity constraint.

7 pages, Invited talk at the 21st meeting of the Astronomical Society of India, Feb 5 - 8, IUCAA, Pune. To be published in the Bulletin of the Astronomical Society of India

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