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IceCube - FAQ

What are neutrinos?

Neutrinos are subatomic particles produced by the decay of radioactive elements and elementary particles that lack an electric charge. They are emitted when neutrons transform into protons in nuclear reactions such as those of the sun or in the collapse of a dying star. Other than particles of light, neutrinos are the most common particle in the universe. They are so tiny that they can pass through solid matter without colliding with any molecules and they travel at nearly the speed of light, making them incredible intergalactic messengers.

Learn more about neutrinos, the different types and their origin, as well as about the fascinating history that lead to their discovery here.

What are you hoping to find?

IceCube detects the blue light emitted by the nuclear reaction of a single neutrino crashing into an ice atom. We are looking for neutrinos of extremely high energy, emitted from supernova explosions, gamma-ray bursts, black holes, and other extra-galactic events. Correlating the number and intensity of the detected high-energy neutrinos with these events will help us understand the nature or the events, as well as the sources of dark energy and dark matter. Neutrinos are attractive for high-energy astronomy because they are not absorbed in dense sources like other probe particles, and they travel in straight lines from their source.

Why is this important?

Our principal motivation is curiosity—the dream of mankind understandings its origins, our place in the cosmos, and foreseeing a future far beyond our human horizons. We are looking to unlock the secrets of our universe; specifically what powers the most energetic engines in the cosmos that fuels the bombardment of cosmic rays to Earth. We want to understand the nature of dark matter. Ultimately, the matter from which we are made is only 4 percent of the Universe's inventory, whereas dark matter comprises 23 percent.

But this is not the full story. As history teaches us, purely exploratory research eventually leads to other discoveries. Even before the IceCube project was completed, scientists have been able to glean useful information from the detector. Because the telescope is constantly bombarded by other particles, including many generated by cosmic rays, University of Wisconsin-Madison researchers Rasha Abbasi and Paolo Desiati, with collaborator Juan Carlos Díaz-Vélez, recognized an opportunity in the cosmic ray data. "IceCube was not built to look at cosmic rays. Cosmic rays are considered background," Abbasi says. "However, we have billions of events of background downward cosmic rays that ended up being very exciting." And this, we suspect, is just the beginning.

Why build it at the South Pole?

For optimal operation of the IceCube telescope, we needed to find the clearest, purest ice in as large a quantity as possible. Most ice has air bubbles that would distort our measurements. The South Pole, being essentially an enormous glacier, is comprised of tightly compressed ice. The immense pressure forces out the air bubbles, rendering ice in its purest form.

IceCube detects blue light emitted by the nuclear reaction initiated by a direct hit of a neutrino on an atom of ice. Because these hits are rare, it requires a lot of ice atoms to capture an event; actually, a cubic kilometer of ultra transparent ice is needed to do the science. The detector has to be shielded from the natural radiation at the Earth’s surface; consequently, there is 1.5 kilometer of ice covering the IceCube detector. The South Pole station constructed on three kilometers of clear ice presented us with an opportunity to satisfy all the requirements needed to build a detector of this complexity and make neutrino astronomy a reality.

How big is the telescope?

IceCube covers one cubic kilometer. The top of the array of detectors is buried in the ice at a depth of 1400 meters (4,593 feet).

How much did it cost to build?

The total cost of the project was $271 million USD.

Who provided the funding?

The National Science Foundation (US) provided majority of the money for construction, about $242 million. Another $30 million came from funding agencies in Germany and Sweden.

How do you maintain the sensors?

Once the detectors are frozen in the ice, they can no longer be physically accessed. We are very careful about testing the Digital Optical Modules (DOMs) before they are deployed into the ice for this reason. We are, however, able to troubleshoot electronic problems and update software remotely, since all DOMs are wired to the IceCube Lab at the South Pole.

How many people are involved?

World-wide over 400 people have been involved in the construction of the observatory, the development of the data analysis tools, and the analysis of the data obtained thus far.

How many people actually winter over?

Three people spend the entire year (winter over) at the South Pole for IceCube. Their jobs are to maintain the data acquisition computers and collect data. About 50 people stay the whole year out of all the projects located at the South Pole.

How many people go to the South Pole for just the summer?

During the construction period, between November 1 and February 15, about 100 people from the IceCube project went to the South Pole—although they were not all there at the same time. Only about 48 people from IceCube are there at any one time. The average population of all scientists and support people at the South Pole during the Austral Summer is about 150 people.


Prof. Olga Botner
Prof. Allan Hallgren

Lägerhyddsvägen 1
752 37 Uppsala

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