Cosmic magnetism revealed
Jan 5, 2006
Japanese physicists may have solved a longstanding mystery in cosmology -- how the large-scale magnetic fields found in today's galaxies and galaxy clusters were initially created. Kiyotomo Ichiki at the National Astronomical Observatory of Japan and colleagues suggest that these fields originated in the very early universe from interactions between photons and electrons before the first atoms had time to form. The fields produced may have been strong enough to affect the formation of early stars, says the team (Sciencexpress 1120690).
Scientists are still unsure about where the substantial magnetic fields in the present-day universe came from. These fields are estimated to be about a micro-Gauss (roughly one millionth of the Earth's magnetic field). Current models can only explain the origin of these fields on small cosmological scales, such as in stars or in supernova explosions, and run into difficulty when faced with larger scales like those found in galaxies and galaxy clusters.
In the early universe, ordinary matter consisted of a hot plasma containing protons, electrons and photons, in which the density of photons fluctuated in space. According to Ichiki and colleagues, this caused a "wind" of photons to blow from high- to low-density regions. These photons "pushed" the electrons, but not the protons, which are much heavier. This process set up rotating electric currents that in turn generated "seed" magnetic fields. The team thinks that this phenomenon occurred before the universe cooled down enough for the protons and electrons to recombine and form the first atoms.
The Japanese reserachers calculated how the density of photons, electrons and protons fluctuated during this period and evaluated the size of the induced electric currents. They found that the magnetic fields subsequently produced were 10-16.8 Gauss at megaparsec scales (about 3.3 x 106 light years) and 10-12.8 Gauss at kiloparsec scales (around 3.2 x 104 light years). These fields, which may have amplified over time to achieve the values observed today, might have been large enough to affect how the first stars formed.
The physicists say that cosmologically generated magnetic fields could now be used as a new tool to investigate the early universe. Moreover, the team predicts that the magnetic fields should exist even in vacant regions of space that do not contain stars or galaxies. "We are very interested in testing our theory by directly observing magnetic fields in such regions," says Ichiki.
About the author
Belle Dumé is science writer at PhysicsWeb