Space + Flight

22
Nov

An Icy Neutrino Observatory

Usually, astrophysicists have their minds fixed on the heavens. But now, they’re are keeping a watchful eye on the icy shield that covers one of the most frigid, remote places on Earth—the South Pole.

There, they’ve built an outpost packed with 5,000 sensors designed to detect neutrinos, the fleeting subatomic particles that fly through our bodies at a rate of a trillion times a second. Neutrinos rarely interact with normal matter, which makes them extremely difficult for physicists to identify. One option is to build a big detector to increase the likelihood of collisions, and the IceCube Observatory—a $271 million endeavor—appears large enough to do the trick. So why Antarctica? Here’s Kenneth Chang, writing for the New York Times:

Once in a great while, a neutrino does collide with something, setting off a cascade of electrons and other subatomic debris. Charged particles in a transparent material like ice give off blue light. Phototubes record the bursts of light, and from the patterns, scientists can determine the direction and energy of the incoming neutrinos.

icecube-observatory
Antarctica's IceCube Observatory is searching for neutrinos from the outer reaches of space.

IceCube’s mission is to catch neutrinos from the outer reaches of space as they pass through the Earth. This type of neutrino—as opposed to the kind cooked up by our sun during fusion—can provide astronomers with information about the calamitous events that happen thousands of light-years away. But separating these from more prosaic solar neutrinos is anything but easy.

Here’s John Timmer, writing for ArsTechnica:

Cosmic rays slam into the atmosphere all the time, and these can produce neutrinos that then enter the ice cap. They can also produce other exotic particles that produce light as they pass through the ice. Muons, for example, only live about 10-6 seconds, but they’re moving so fast that time dilation means they live longer from the Earth’s frame of reference. As a result, they may travel several kilometers through the ice before decaying.

To handle these cases of background, the authors eliminated any signals that were present in the outermost edges of the detector. Cosmic rays are especially easy to spot given that they tend to produce a spray of particles, many of which will be found at the detectors closest to the surface. You might still get a few neutrinos created above the North Pole and passing through on their way out of Earth, but the authors found that the majority of their signals came from the south, suggesting that these neutrinos aren’t a major problem for this detector.

Francis Halzen, a physics professor at the University of Wisconsin, reported in the journal Science that he and his team had discovered 26 new neutrinos that hadn’t originated from the sun in addition to the two announced earlier this year, named Bert and Ernie. (All 28 were named after Sesame Street characters; Bert and Ernie were the most energetic.)

The first and only other successful neutrino detection occurred in 1987, when detectors in the U.S., Japan, and Russia found two dozen of them originating from a supernova about 165,000 light-years away. Now that IceCube is up and running, though, scientists hope an avalanche of data awaits them.

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