The weather outside may be frightful where you are but at least it’s not -30 degrees Celsius. Yet in these sub-zero conditions, researchers at the South Pole have placed the final string of detectors for the Icecube Neutrino Observatory, a cubic kilometer-sized telescope meant to search for the origin of cosmic rays, on 18 December.

Icecube, which has been under construction since 2005, is composed of 86 wires set in the Antarctic ice at depths ranging from 1,450 to 2,450 meters, each with 60 basketball-sized detectors strung on them like Christmas lights. The detectors look for a characteristic blue flash of light, which signals that a neutrino has hit an oxygen atom. Such events are rare—trillions of neutrinos may pass through the ice without interaction—but each flash tells researchers where the neutrino came from and how much energy it had.

To build the telescope, researchers drilled holes in the ice with a jet of near-boiling water flowing out of a hose at around 760 liters/minute, explains Albrecht Karle, a physicist at the University of Wisconsin in Madison. At that rate, it takes nearly a day to drill the full 2450 meters and, after inserting the detectors, the researchers wait five to six days for the hole to refreeze before they can begin taking data, he adds.

Within a few weeks the entire array will be completely frozen and, after calibration, data will be taken with the full array beginning around 1 May, says Karle. Aside from investigating the origin of high-energy cosmic rays, Icecube may shed light on the nature of dark matter and could even provide evidence for the extra dimensions predicted in string theory, says Spencer Klein, a physicist at the Lawrence Berkeley National Lab in Berkeley, California.