Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003basbr..23...62k&link_type=abstract
Boletim da Sociedade Astronômica Brasileira (ISSN 0101-3440), vol.23, no.1, p. 62-62
Astronomy and Astrophysics
Astronomy
Scientific paper
Large scale magnetic fields in galaxies are thought to be generated by a turbulent dynamo. However, this same turbulence also leads to a dynamo which generates small scale magnetic fields at a more rapid rate. The efficiency of the large scale dynamo depends upon how the small scale magnetic fields saturate. We examine this issue for the first objects formed in the universe, after recombination and before re-ionization. Ambipolar diffusion might play a significant role in the saturation of the small scale magnetic fields, due to the low level of ionization of the gas. By numerically integrating the evolution equations for the large and small scale dynamos, we show that: 1) For a low enough ion density, ambipolar diffusion is efficient enough to suppress the growth of small scale magnetic fields, thus allowing the large scale dynamo to operate for a longer time. 2) The growth rate and features of the large and small scale fields strongly depend on the turbulence spectrum: for a spectral index n = 4/3 (Kolmogorov turbulence), the field saturates faster than for n > 4/3 (intermittent turbulence). These effects help to enhance a magnetic seed field in the first structures formed in the universe and, hence, provide a larger seed field for dynamo action in the structures existing after reionization.
Barros Saulo M. R.
Kandus Alejandra
Opher Reuven
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