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Originally published in Science Express on 5 January 2006
Science 10 February 2006:
Vol. 311. no. 5762, pp. 827 - 829
DOI: 10.1126/science.1120690
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Reports

Cosmological Magnetic Field: A Fossil of Density Perturbations in the Early Universe

Kiyotomo Ichiki,1,2* Keitaro Takahashi,3 Hiroshi Ohno,4 Hidekazu Hanayama,1,5 Naoshi Sugiyama1

The origin of the substantial magnetic fields that are found in galaxies and on even larger scales, such as in clusters of galaxies, is yet unclear. If the second-order couplings between photons and electrons are considered, then cosmological density fluctuations, which explain the large-scale structure of the universe, can also produce magnetic fields on cosmological scales before the epoch of recombination. By evaluating the power spectrum of these cosmological magnetic fields on a range of scales, we show here that magnetic fields of 10–18.1 gauss are generated at a 1-megaparsec scale and can be even stronger at smaller scales (10–14.1 gauss at 10 kiloparsecs). These fields are large enough to seed magnetic fields in galaxies and may therefore have affected primordial star formation in the early universe.

1 National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan.
2 Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA.
3 Department of Physics, Princeton University, Princeton, NJ 08544, USA.
4 Corporate Research and Development Center, Toshiba Corporation, Kawasaki 212-8582, Japan.
5 Department of Astronomy, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

* To whom correspondence should be addressed. E-mail: ichiki{at}th.nao.ac.jp

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Science. ISSN 0036-8075 (print), 1095-9203 (online)