The IceCube Neutrino Observatory at the South Pole was the first to discover ultrahigh-energy neutrinos which most likely were the result of cosmic acceleration in outer space. “After more than a decade of intense searching, we can now announce that we have found neutrinos that were very probably generated in the vast expanses of outer space”, reported Professor Lutz Köpke of Johannes Gutenberg University Mainz (JGU). Neutrinos are electrically neutral particles with tiny mass. High-energy neutrinos may be generated in the proximity of black holes and are subsequently accelerated to acquire their extraordinary energies. They can then travel through space almost completely unhindered. On the downside, they are very difficult to detect. The IceCube experiment has now found 28 neutrinos with energy greater than 50 tera-electron volts (TeV) all of which landed in the Antarctic ice between May 2010 and May 2012. “This discovery was one of the key objectives of the IceCube experiment. It is fantastic that we have now reached this milestone, and in a way it is a relief as well,” said Köpke, who has been searching for astrophysical neutrinos for more than 13 years and served as an internal reviewer as the final analysis was scrutinized.The IceCube Neutrino Observatory is composed of 5,160 optical sensors placed in the Antarctic ice. Together they cover one cubic kilometer of clear South Polar ice. The high-precision optical sensors can detect weak flashes of blue light, also known as Cherenkov radiation, which is generated if neutrinos react near a detector and produce charged particles. The detector was completed in late 2010 and provides data around the clock. It is currently the largest facility designed to search for neutrinos from outer space.

The IceCube Neutrino Observatory is composed of 5,160 optical sensors placed in the Antarctic ice. Together they cover one cubic kilometer of clear South Polar ice. The high-precision optical sensors can detect weak flashes of blue light, also known as Cherenkov radiation, which is generated if neutrinos react near a detector and produce charged particles. The detector was completed in late 2010 and provides data around the clock. It is currently the largest facility designed to search for neutrinos from outer space.

Even though a few neutrinos were discovered in 1987 after the explosion of a supernova in the Large Magellanic Cloud, their energy was about a million times less than the particles that were justdiscovered. “Some of the neutrinos we have now detected have a thousand times more energy than neutrinos created in particle accelerators on earth,” explained Köpke. “Only a third of the 28 high-energy neutrinos could have been generated by cosmic radiation in the Earth’s atmosphere.”

Milliarden von Neutrinos durchdringen jeden Quadratzentimeter auf der Erde. Die meisten entstehen in der Sonne oder in der Erdatmosphäre, die laufend mit kosmischer Strahlung bombardiert wird. Viel seltener stammen Neutrinos aus entfernten Regionen in- und außerhalb unserer Galaxie. Die Existenz dieser Neutrinos und die Vorgänge, die zu ihrer Entstehung in der Nähe von Supernovae, schwarzen Löchern, Pulsaren, aktiven Galaxien sowie weiteren extremen extragalaktischen Phänomenen führen, wurden in vielen wissenschaftlichen Arbeiten erörtert. Das IceCube-Observatorium wurde insbesondere entwickelt, um Häufigkeit und Art der vorhergesagten hochenergetischen Neutrinos sowie ihre Herkunft zu untersuchen.

The findings with a significance greater than four standard deviations now published in Science illustrate that the neutrinos observed have properties that clearly indicate an origin in cosmic accelerators. “The decisive analysis was carried out by a group of postdoctoral researchers and doctoral candidates at the University of Wisconsin in Madison, Wisconsin, USA, two of whom were German. Work is now being done to improve the precision of the observations and to understand what the signal means and where it comes from,” explained Köpke.

The IceCube Neutrino Observatory at the geographic South Pole was completed in December 2010 after seven years of construction, on time and within budget. The American National Science Foundation (NSF) financed the instrumentation and the German Federal Ministry of Education and Research (BMBF) provided sizable funding for the experiment and the scientific personnel needed to conduct it. The project includes 250 physicists from the US, Germany, Sweden, Belgium, Switzerland, Japan, Canada, New Zealand, Australia, the United Kingdom, and Korea. Professor Lutz Köpke’s work group at Mainz University is part of the “Precision Physics, Fundamental Interactions and Structure of Matter” (PRISMA) Cluster of Excellence.