Giant magnetic fields in the universe

Print edition : April 14, 2017

Using the 100-m radio telescope at Effelsberg, Germany, astronomers from Bonn and Tautenburg in Thuringia observed several galaxy clusters. At the edges of these accumulations of dark matter, stellar systems (galaxies), hot gas and charged particles, they found magnetic fields that are exceptionally ordered over distances of many millions of light years, making them the most extended magnetic fields in the universe known so far. The results will be published in the latest issue of the journal Astronomy & Astrophysics.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e., 100 times the diameter of the Milky Way, they host a large number of such stellar systems, along with hot gas, magnetic fields and charged particles. These systems are believed to be embedded in large haloes of dark matter, the composition of which is unknown. Collision of galaxy clusters leads to a shock compression of the hot cluster gas and of the magnetic fields. The resulting arc-like features are called “relics” and stand out by their radio and X-ray emissions. Since their discovery in 1970 with a radio telescope near Cambridge, U.K., relics have been found in about 70 galaxy clusters so far, but many more are likely to exist. They are messengers of huge gas flows that continuously shape the structure of the universe.

The compression of magnetic fields orders the field lines, which also affects the emitted radio waves and makes them linearly polarised.

This effect was detected in four galaxy clusters, in one case for the first time, by a team of researchers at the Max Planck Institute for Radio Astronomy in Bonn (MPIfR), the Argelander Institute for Radio Astronomy at the University of Bonn (AIfA), the Thuringia State Observatory at Tautenburg (TLS), and colleagues in Cambridge, Massachusetts, in the U.S.

They used the MPIfR’s 100-m radio telescope near Bad Munstereifel-Effelsberg at wavelengths of 3 cm and 6 cm. Such short wavelengths are advantageous because the polarised emission is not diminished when it passes through the galaxy cluster and the Milky Way.