The last Digital Optical Module (DOM) is being deployed in the IceCube detector.

Culminating a decade of planning and six years of construction, the neutrino telescope “IceCube” was completed on 18 December 2010. The world’s largest particle detector fills a cubic kilometer of deep Antarctic ice containing ultrasensitive light sensors. They record the tracks from neutrinos coming from outer space, to get information about distant galaxies from these astronomical messengers. Neutrinos are often called “ghost particles” because they pass undetected through most matter. Thus, enormous detectors are needed to prove their existence.

At the geographic South Pole, IceCube is embedded in the deep ice below the United States’ Amundsen Scott Station. IceCube consists of 86 strings, each carrying 60 glass speres, deployed in depths between 1.45 and 2.45 kilometres. The speres protect ultrasensitive light sensors to record the tiny flashes of blue light emerging from neutrino reactions. A quarter of a total of 5000 optical sensors were provided by German research groups, previously assembled and tested at the DESY research centre in Zeuthen. The project is conducted by an international consortium headed by the US National Science Foundation (NSF). The NSF also funded most of the construction costs amounting to 279 million US dollars.

With its crystal clear deep ice and the excellent infrastructure offered by the Amundsen Scott station, South Pole is an ideal location for this project. Installation work is done in the Antarctic summer from November through February, when the sun shines 24 hours a day and the temperature rises to passable minus 30 Centigrade. The holes into which the speres are deployed are drilled into the ice with hot water of 80 Centigrade. After delpoying one string with optical sensors, the water in the hole freezes within a few days.

Neutrinos are elementary „ghost“ particles that had been predicted in 1930, but were detected only in 1956. Every second, trillions of them bombard every square centimetre of the world’s surface, most of them streaming through the earth without colliding with a single atom. Because they rarely interact with regular matter, neutrinos are difficult to detect but, on the other hand, they easily escape compact cosmic regions like the inner part of the sun and travel undisturbed through the universe, thus becoming unique cosmic messengers. IceCube searches for neutrinos from sources with a distance of thousands or billions of light years. Research objects are dark holes located in the centre of galaxies that attract matter like a maelstrom, and mysterious dark matter which fills our universe, but could so far not be identified.

The IceCube team before deploying the last sensor.

Dr. Christian Spiering from the DESY research centre, long-time European coordinator of the IceCube forerunner project and IceCube spokesman from 2005 to 2007, eagerly looks to the future: “Now, IceCube has reached its full sensitivity, and we are looking forward to soon discover extraterrestrial sources of highly energetic neutrinos. Already this year’s scientific results are impressive. We were able to register nearly one hundred thousand neutrinos coming from earth’s atmosphere, some with energies up to 400 Tera Electronvolts. This is a thousand times more than the energy from neutrinos produced in accelerators on earth. The existing data already cause some excitement: a strange pattern in the directional distribution of cosmic rays, with its explanation still pending.”

The IceCube team consists of 260 scientists from 36 research institutions in 8 countries. German institutions are: Deutsches Elektronen-Synchrotron DESY, the universities RWTH Aachen, Humboldt-Universität zu Berlin, Bochum, Bonn, TU Dortmund, Mainz and Wuppertal, and the Max Planck Institute for Nuclear Physics in Heidelberg. Apart from a quarter of the optical modules, the German participants contributed a significant part of the receiver electronics on the ice surface. The German share of about 20 million € was funded by the Federal Ministry of Education and Research, the Helmholtz Association, the German Research Foundation, and by the normal budgets of the universities.

Photos of IceCube completion