Detecting neutrinos at the South Pole.
Research site: IceCube Neutrino Observatory, Antarctica
What?► Where in the cosmos are the violent supernovae and super-massive black hole cataclysms that create the very high-energy neutrinos that bombard and pass right through the earth? That is what 45 institutions and 300 scientists from 12 countries are attempting to discover at the South Pole Neutrino Observatory.
Around 100 trillion neutrinos pass right through your body every second as the near-massless particles interact only very weakly with matter, colliding infrequently with atoms. That makes them incredibly hard to detect, says Elisa Resconi, a physicist at the Technical University of Munich (TUM). And that means, she says, that an observatory seeking to sense even the high-energy neutrinos from supernovae need a whole new approach to astronomy.
Until now most astronomy has involved the detection of photons: radio waves, ultraviolet, infrared, visible light or high-energy gamma rays. Adding neutrino detection to the picture offers another advantage, says Resconi: it gives
scientists an entirely different picture of the universe. “For instance, the photons reaching the earth from the Sun are coming from its surface. But neutrinos are coming from fusion reactions at its core. So we are looking at the Sun in an entirely different way.”
How?► In the IceCube Neutrino Observatory – a cubic kilometre of ice, equal in volume to one million swimming pools of water, at the South Pole. An initiative of the University of Wisconsin, IceCube has been peppered with more than 5,000 detectors, called photomultipliers, in a 3D matrix than can sense the ultraviolet Cherenkov radiation emitted when a high-energy neutrino collides with an atom. Holes drilled in the ice with hot water drills have allowed the sensor array to be placed between 1.5 and 2.5 km below the surface to prevent interference from atmospheric neutrinos: the cosmic ones of interest actually power through the earth from the North Pole.
Completed in 2010, IceCube made its first major discovery
More about Neutrinos!
With the Borexino experiment, physicists at Technische Universität München (TUM) have been able to gain a direct insight into the core of the Sun for the first time and explore how it generates energy. This success was enabled by a custom-built experimental set-up with the lowest levels of radioactivity on Earth.
in 2013 when an analysis showed that it had sensed 28 ultra-high-energy neutrinos from sources outside our solar system. Such results make the work of Resconi’s colleagues at the South Pole extremely “emotional, challenging and intellectually fascinating”, she says. It is her role to decide which of her 10 staff go to the Antarctic for two to three months at a time to tend TUM’s part of the IceCube experiments – and it is a popular posting. “They are eager to go there and they are very motivated about the science.” TUM physicist Martin Jurkovic spent two months at IceCube in 2014. “It was so exciting to get off the plane at the South Pole to find the temperature was -45 °C,” he says. “The air pressure is low, equivalent to an altitude of 3,200 metres, so if you do any exercise you have to catch your breath.” His strongest memory of the extreme science site? The sheer beauty of the snow sculptures built up around the observatory by the wind. “They are just gorgeous,” he says.
Special report by Paul Marks
Karin Sigloch, Geophysicist (2/5)