World's largest neutrino observatory completed in Antarctica
By Ben Coxworth
December 20, 2010
After five years of construction, an international team has put the finishing touches on the University of Wisconsin’s IceCube Neutrino Observatory. Located in Antarctica, the observatory is looking specifically for high-energy neutrinos, which are created in violent cosmic events such as super novae and gamma ray bursts. As neutrinos collide with water molecules in the pitch black, ultra-clear ice, a blue flash of light results, which is detected by the sensors. Ever since neutrinos were discovered in 1956, scientists have hoped to decipher the information these astronomical messengers carry about distant cosmic events and the completion of the observatory marks an important step towards tracing their origins.
The business end of the observatory consists of 5,160 optical sensors that have been joined together in groups of 60 on a total of 86 “strings.” Each string has been lowered into an individual vertical bore hole in the Antarctic ice cap, the holes arranged in a grid. Now that all the strings are frozen in place, the sensors on them make up a one-square-kilometer cube-shaped matrix, the top of which sits 1.24 miles (2 km) below the surface of the ice.
To get the project finished on time and on budget, crews worked around the clock, as construction was limited to the summer months of November through February. Even then, all personnel and supplies had to first be flown into the McMurdo research station, then transported 800 miles (1,287 km) by C-130 cargo aircraft to the National Science Foundation's Amundsen-Scott South Pole Station. The observatory is located in the ice beneath that facility.
In order to bore the holes in the ice, U Wisconsin scientists created a 4.8-megawatt Enhanced Hot Water Drill. By focusing a jet of hot water into the ice, the device was able to bore over 1.24 miles (2 km) down per day. Although it was completed only last week, IceCube has been gathering data since construction began in 2005. As more strings of sensors were added, the amount of data that could be gathered increased.
“Even in this challenging phase of the project, we published results on the search for dark matter and found an intriguing pattern in the arrival directions of cosmic rays,” said principal investigator Prof. Francis Halzen. “With the completion of IceCube, we are on our way to reaching a level of sensitivity that may allow us to see neutrinos from sources beyond the sun.”
All images courtesy University of Wisconsin