Frequently Asked Questions
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- What are neutrinos?
- What are you hoping to find?
- Why is IceCube important?
- Why build IceCube at the South Pole?
- How big is IceCube?
- How much did it cost to build?
- How do you maintain the sensors?
- Who is in charge of the detector?
- How many people are involved?
- How many people actually winter over?
- How many people go to the South Pole for just the summer?
Neutrinos are invisible, nearly massless subatomic particles that are electrically neutral. They can travel at nearly the speed of light from the edge of the universe without being deflected by magnetic fields or absorbed by matter. They travel in straight lines from their source. This makes them excellent messengers of information about the objects or events in which they originate.
Neutrinos originate in some of the most violent and least understood events in the universe. Events like supernovas and objects like active galactic nuclei and black holes are just a few possible sources of high-energy neutrinos. Other than particles of light, called photons, neutrinos are the most common particle in the universe.
IceCube detects light emitted by charged particles that are produced when a single neutrino crashes into a proton or neutron inside an atom. The resulting nuclear reaction produces secondary particles travelling at high speeds (faster than light in the ice!) that give off a blue light called Cherenkov radiation. The neutrinos we detect are like fingerprints that help us understand the objects and phenomena where the neutrinos are produced.
IceCube is fundamental research, and pure exploratory research usually leads to other astounding discoveries. As IceCube gives us new ways to study the mysteries of our universe, it is likely to uncover or lead to the discovery of things we couldn’t have anticipated.
For example, roughly 4% of our universe is made up of regular matter like atoms and molecules. The other 96% of our universe is made of a material we can’t see and that we barely understand. It is comprised of dark matter (23%) and dark energy (73%). Neutrinos may give us a better understanding of dark matter and dark energy.
In order to detect the light given off by the secondary particles produced by neutrino interactions, we needed a large volume of transparent material. That basically meant water or ice. Because these interactions are rare and produce light that can extend over a kilometer, IceCube requires a lot of ice atoms to capture one event. The South Pole is the one place on Earth that holds such large quantities of clear, pure, and stable ice and has the infrastructure to support scientific research.
Most ice contains air bubbles that would distort IceCube’s measurements, but the South Pole ice sheet is very thick and tightly compressed. As snow and ice piled up over time, the lower layers of ice were compressed. The immense pressure forced out air bubbles, making the deep ice ultra-transparent.
IceCube not only needs clear, pure, and stable ice to make its discoveries; it also needs to be shielded from radiation at the Earth’s surface. IceCube’s individual sensors, called digital optical modules, or DOMs, are buried in the ice beginning at a depth of about 1,500 meters (4,920 feet, almost a mile) below the surface. The 1,500 meters of ice above the detector help to shield it from natural radiation at the Earth’s surface.
The South Pole station, constructed on three kilometers of clear ice, presented an opportunity to satisfy all the requirements needed to build the detector.
IceCube covers one cubic kilometer. It has an area of approximately 1 square kilometer and is 1,000 meters deep, with the top of the detector array buried in the ice at a depth of about 1,500 meters (4,920 feet).
The total cost of the project was $279 million USD. The National Science Foundation provided the majority of the money for construction, about $242 million. The remaining funds came from funding agencies in the US and abroad.
The sensors that make up the detector are called digital optical modules, or DOMs, and were carefully tested before they were deployed. Once they are frozen in the ice, they can no longer be physically accessed. We can, however, troubleshoot electronic problems and update software remotely, because all DOMs are wired to the IceCube Lab at the South Pole.
The IceCube Collaboration runs the project and the University of Wisconsin–Madison (UW) is the lead institution. UW led construction of the IceCube proof-of-concept project called AMANDA, and in evaluating proposals from several institutions, the National Science Foundation determined that UW had the experience and success to oversee IceCube.
About 300 physicists, computer scientists, and engineers make up the IceCube Collaboration, from 45 institutions in 12 countries as of September 2014.
IceCube has two people who spend the entire year (winter over) at the South Pole. Their jobs are to maintain the data acquisition computers and collect data. About 40 people in other science and support positions stay at the South Pole station for the long, dark winter.
During IceCube’s construction from 2004 to 2011, about 100 people working on IceCube would be at the South Pole between November 1 and February 15. However, they were not all there at the same time. Only about 48 people from IceCube were there at any one time during its construction. The average population of all scientists and support personnel at the South Pole during the austral summer is about 150 people.