Deep beneath the Antarctic ice, scientists are catching some of the most energetic particles in the universe. The IceCube Neutrino Observatory, a detector frozen into one cubic kilometer of clear ice at the South Pole, records faint flashes that reveal the arrival of neutrinos. These elementary particles have no electric charge and almost no mass, and because they barely interact with anything they are often called ghost particles. According to a report from the University of California San Diego, some neutrinos detected at IceCube carry roughly 10 billion times the energy of a typical neutrino from the Sun. One detected by a similar experiment had 200 times more energy, and no one knows where it came from.
The news follows this year's Nobel Prize in Physics, awarded to physicist Francis Halzen for decisive contributions to IceCube and to the discovery of high-energy neutrinos of astrophysical origin. Neutrino research has now contributed to five Nobel Prizes. These ultra-energetic particles are among the observatory's most exciting results, because their origins and the processes that accelerate them remain a mystery.
How do you catch a ghost particle?
Neutrinos are detected only on the rare occasions when one strikes matter through the weak interaction, a fundamental force about 20 orders of magnitude weaker than electromagnetism. In IceCube, such a collision can produce a fast-moving charged particle, such as a muon, which travels through ice faster than light moves through it and emits a blue glow called Cherenkov radiation. Strings of light sensors lowered deep into the ice record these glows, letting researchers estimate each neutrino's energy and arrival direction. Only a few dozen of the most energetic cosmic neutrinos are caught each year.
This research matters because neutrinos are messengers from places nothing else can escape. They stream out of collapsing stars and the neighborhoods of black holes, carrying information that light cannot deliver. Related work at the Simons Observatory in Chile's Atacama Desert studies the cosmic microwave background, the oldest light in the universe, and may also reveal information about neutrinos from the universe's earliest moments.