IceCube: how the South Pole became a neutrino detector

An observatory near the South Pole is built from ice and light detectors. NASA's Astronomy Picture of the Day reports that almost 100 holes have been melted into the ice there and are now used for astronomy. The site is the IceCube Neutrino Observatory.

The setup is the same at every hole. Astronomers lower a long string into each vertical shaft of water. The string is knotted with light detectors, each about the size of a basketball. Then the water refreezes and holds them in place.

What the detectors are watching for

Frozen into clear ice, the detectors are sensitive to blue light. That light is a leftover from a collision. High-energy neutrinos reach the ice from powerful processes elsewhere in the universe, strike ice molecules, and set loose fast-moving secondary particles that produce the blue glow.

APOD reports that IceCube has detected many of these neutrinos. With its strings in place, APOD describes it as the largest neutrino detector ever created. The explanation accompanies a photograph from 2010, when crews lowered one of IceCube's final detector strings.

The Nobel Prize

**Reported:** A founding leader of the IceCube Collaboration is to receive the Nobel Prize in Physics, an award announced earlier this week. APOD's explanation does not name the recipient or say who made the announcement, so those details are still to come.

Can you see it?

No. There is nothing overhead to look for here. IceCube sits in ice near the South Pole, and the neutrinos it catches come from powerful processes far from Earth rather than from anything you could point binoculars at.

The numbers do give you a sense of scale. Nearly 100 holes. A detector the size of a basketball at every knot. All of it melted, lowered into the water and left to freeze.

• Astronomy Picture of the Day
• IceCube
• neutrinos
• Nobel Prize in Physics
• South Pole