Basically the only existing theories for the creation of a magnetic field B in the Universe are the creation of a seed field of order 10^{ -20} G in spiral galaxy which is subsequently supposedly amplified up to the observed 10^{ -6} - 10^{ -5} G by a dynamo process or a seed intergalactic field of magnitude 10^{ -12} - 10^{ -10} G which is amplified by collapse and differential rotation. No satisfactory dynamo theory, however, exists today. We show that a 10^{ -6} - 10^{ -5} G magnetic field in spiral galaxies is directly obtained from a nonminimal gravitational-electromagnetic coupling, without the need of significant dynamo amplification.
Categories: astro-ph gr-qc