The Universe in Another Light

13/07/2018
Jan Auffenberg/RWTH

Together with the other research teams of the ICE Cube Experiment, a team of RWTH physicists led by Professor Christopher Wiebusch from the Institute of Physics IIIB, made a unique discovery. They located a source of cosmic high-energy neutrinos, which travel billions of light years though space and easily traverse planets like the earth. An individual, spectacular neutrino detected by the IceCube neutrino telescope, located at the South Pole in Antarctica, on September 22, 2017, initiated a joint observation campaign involving 18 observatories. The results were now published in the “Science” academic journal.

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The observations provide an important step towards finding the solution to an old mystery: Where does cosmic radiation come from? “Now, we are able to give more precise answers,” says Wiebusch. His research assistant René Reimann, who played a major role in achieving this result, adds: “We were are able to detect a neutrino and trace its origin back to the extremely high-energy galaxy designated TXS-0506+056, which is located in the constellation of Orion. It became really exciting when we were sifting through the archived data of almost ten years of oberservations: we found a second neutrino eruption in 2015 from the same source.

About five years ago, IceCube succeeded in detecting high-energy neutrinos from the depths of space for the first time. The directions from which they came seemed to be randomly distributed. As Wiebusch concludes, “This earlier eruption, in combination with the individual event dated September 22, 2017, provides the best experimental evidence that active galaxies are the source of high-energy cosmic particles.”

Messengers from the High-Energy Universe

The researchers assume that these energy-rich neutrinos are generated as a characteristic byproduct of cosmic particle accelerators, which may take the form of swirling vortices around gigantic black holes or of exploding stars. By contrast with electrically charged atomic nuclei, the electrically neutral neutrinos are not deflected on their way through space by cosmic magnetic fields, so that the straight path they are travelling points to their origin.

To detect neutrinos is extremely difficult, as the "ghostly“ elementary particles may traverse the earth without even leaving a trace. It is only very rarely that a neutrino interacts with matter. It requires enormous detectors to capture just a few of these rare reactions. “For this reason, we drilled 86 holes, each 2,500 meters deep, into the ice of Antarctica. 5,160 slight sensors were installed in these holes and spread out over one cubic kilometer. They can register tiny flashes of light produced when neutrinos interact with the transparent ice they are suspended in,” explains RWTH physicist Dr. Jan Auffenberg.

The IceCube Collaboration

The international IceCube collaboration consists of about 300 researchers from twelve countries. The National Science Foundation (NSF) provided the primary funding for the observatory, with assistance from partner funding agencies around the world. The University of Wisconsin-Madison is the lead institution, responsible for the maintenance and operations of the detector.

After the US research group, the team German researchers constitute the second largest team in the collaboration. Next to Deutsches Elektronen-Synchrotron, DESY for short, nine German universities contribute to the project: RWTH Aachen University, HU Berlin, Ruhr-Universität Bochum, TU Dortmund University, the University of Erlangen-Nürnberg (FAU), the University of Münster, TU Munich, and the University of Wuppertal. The participating German teams receive funding from the Ministry of Education and Research, The Helmholtz Association, the German Research Foundation DFG, and the contributing universities.