New evidence for strong intergalactic magnetic fields may help to solve the mystery of ultrahigh-energy cosmic rays. These particles can reach energies of more than 1020 eV - 100 million times as high as particle beams produced in accelerators on Earth.
At the May meeting of the American Physical Society, Phil Kronberg of the University of Toronto presented low-frequency (75 MHz) radio images of parts of the Great Wall supracluster of galaxies. The observations showed a diffuse synchrotron glow in the regions outside the galaxy clusters, revealing the presence of magnetic fields.
New combined X-ray and radio observations of the clusters has improved the accuracy of measurements of both the magnetic field strength and the density of space in these regions. The team measured the Faraday rotation (the rotation of the plane of polarization) of the radio waves.
The results show intergalactic magnetic fields that are many times stronger than those within the much denser disc of the Milky Way. This means that a significant amount of energy is stored within the intergalactic gas.
This raises important questions about the origin of magnetic fields - whether they were seeded by the first generations of stars and galaxies or result from earlier activity when the universe was less than 1 s old.