What do you get when you drill 86 holes 1.5 miles deep into the frozen ice of the South Pole, install some 5,160 light sensors and network them to a computer system above? In this case you get IceCube, an ice-bound telescope large enough to hold about 1,000 football stadiums that hopefully will be able to gather information on sub-atomic mystery particles called neutrinos.
The collaborative group of scientists that will operate and use the telescope, which has been under construction since 2004, said the telescope needed to be big to capture the rare neutrino collisions with other matter: out of uncounted trillions of neutrinos constantly passing through the ice, IceCube will observe just a few hundred a day, the scientists stated.
University of Wisconsin physics professor Francis Halzen said of neutrinos: "They are just like light; there is basically no difference between neutrinos and light. The only difference is that light doesn't go through a wall whereas neutrinos go through everything. And so just accidentally, they run straight into the nucleus of an atom and then create lots of other particles, which we can see and it's only these accidental crashes of neutrinos that allow us to observe them. That's basically what IceCube is doing."
Such ultra-high-energy neutrinos may be produced in such cataclysmic astrophysical events as violent explosions of gamma-ray bursts and in the energetic particle jets powered by massive black holes. Lower-energy neutrinos are known to come from the Sun, and others at higher energies come from cosmic rays interacting with the Earth's atmosphere and dramatic astronomical sources such as exploding supernovae in the Milky Way and other distant galaxies, the scientists stated.
Key to the $271 million IceCube telescope are its 5,160 basketball-sized detectors known as Digital Optical Modules (DOMs) and their photomultiplier tubes which ultimately will provide the data that lets scientists track neutrino events. "In a lab on the surface of the ice, signals from DOMs on many different strings are combined into a single data stream, which is analyzed to determine the direction and energy of the neutrino events that left their tracks," according to the Berkeley Lab Web site.
"We hope that the neutrinos detected by IceCube will provide the smoking gun that tells us where the cosmic rays are produced, and maybe they also will give us clues about the processes that accelerate them to such high energies," said Tyce DeYoung, an IceCube scientist and an assistant professor of physics at Penn State, one of the IceCube collaborators in a statement. "If we're lucky, we may also find clues about the nature of dark matter, the mysterious stuff that makes up about five times as much of the universe as all the stars, planets, and other normal matter combined."
The IceCube collaboration team includes some 40 affiliated institutions in the US, Germany, Belgium, Sweden, Barbados, Canada, Japan, New Zealand, Switzerland, and the United Kingdom. It was funded largely by the National Science Foundation and is now led by the University of Wisconsin-Madison. The Department of Energy's Lawrence Berkeley National Laboratory has been a major contributor as well.
From the University of Wisconsin, we get these fun facts about the IceCube project:
- Each of the IceCube strings have a theme and each DOM has its own name!
- There are 60 DOMs per string.
- The travel time from Los Angeles to the South Pole is approximately 48 hours.
- The average time to drill a hole for IceCube is approximately 48 hours.
- The time it took to drill IceCube's first hole was 57 hours!
- The average depth of an IceCube hole is 2452 m.
- The average amount of fuel use to drill each hole is approximately 4800 gallons.
- The amount of ice melted per hole is approximately 200,000 gallons.
- The average time to deploy a string is 11 hours.
- The weight of the hose used for the drill is 25,000 lbs!
- Average summer temperatures at the south pole is -18°F.
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