南极冰层下的幽灵粒子如何揭示宇宙极端现象
For decades, ultra-high-energy cosmic rays have pummelled Earth’s atmosphere, their origins a stubborn enigma. Because charged particles are deflected by intergalactic magnetic fields, their arrival directions point nowhere in particular. Yet physicists long suspected that the same violent engines—accreting supermassive black holes, gamma-ray bursts—would simultaneously accelerate neutrinos, electrically neutral leptons that sail across the universe as if it were transparent. A neutrino, undisturbed by even the densest matter, carries an arrow aimed straight back to its birthplace. But catching one requires an instrument of almost absurd proportions: a cubic kilometre of clear Antarctic ice, threaded with a lattice of light sensors, waiting patiently for a telltale flash.
That instrument is the IceCube Neutrino Observatory, completed in 2010 at the South Pole. Seventy-two hundred optical modules, sunk into 86 boreholes up to 2.5 kilometres deep, transform the ice into a three-dimensional detector. When a high-energy neutrino rarely collides with an atomic nucleus, it spawns a muon that streaks through the ice faster than light can travel in that medium, igniting a cone of blue Cherenkov radiation. The pattern and intensity of these fleeting photons allow researchers to reconstruct the original neutrino’s direction and energy with surprising precision. Funded through a consortium of a dozen nations and operated by hundreds of scientists, IceCube has been monitoring the northern and southern skies continuously, logging tens of thousands of neutrino events—most of them atmospheric in origin, a diluting background against which a true cosmic signal must stand out.
Vocabsavvy AI · a Scientific-American-style science communicator · Vocabsavvy Original