2 November 2020, by Heiko Fuchs
Illustration of a distant cluster of galaxies (PSZ2 G091.83+26.11) at 7 billion light years from Earth. The most yellowish-white spots are complete galaxies, some spots are foreground stars. The X-rays (blue) stem from gas of about 10 million to 100 million degrees hot. The radio waves (red) originate from particles that have been accelerated to almost the speed of light.
An international team of researchers with the participation of the Hamburg Observatory of the Universität Hamburg has mapped nine gigantic collisions of galaxy clusters. It is the first time that collisions of such distant clusters have been studied. The researchers publish their findings in the journal “Nature Astronomy”.
Galaxy clusters are the largest structures in the Universe. They can consist of thousands of galaxies, each with billions of stars. When such clusters merge, the electrons between them are accelerated to almost the speed of light. The accelerated particles emit radio waves when they come into contact with magnetic fields in the clusters.
Until now, telescopes were not powerful enough to receive radio waves from distant colliding clusters. But thanks to network of linked antennas of the radio telescope Low Frequency Array (LOFAR) and an 'exposure time' of eight hours per cluster, the researchers were able to collect detailed data from distant clusters for the first time and observe cluster collisions that took place seven billion years ago.
The data shows, among other things, that the radio emission from distant colliding clusters is brighter than previously expected. According to prevailing theories, cluster radio emission originates from electrons that are accelerated by the turbulent motions. It seems that the turbulence and vortices caused by the collisions are strong enough to accelerate particles also in an early Universe.
Furthermore, the magnetic fields in the distant clusters turned out to be about as strong as in previously investigated nearby clusters. According to co-author Prof. Dr. Marcus Brüggen from the Department of Physics of Universität Hamburg this is intriguing: "This work shows for the first time that space is filled with magnetic fields already in a young universe and we do not really know what causes them. In Hamburg we helped design the project and led the theoretical interpretation of the observations."