Summary
High on Greenland’s ice sheet, particle astrophysicists are this week drilling boreholes in a search for the cosmic accelerators responsible for the universe’s most energetic particles. By placing hundreds of radio antennas on and below the surface, they hope to trap elusive particles known as neutrinos at higher energies than ever before. Detectors elsewhere on Earth occasionally register the arrival of ultra–high-energy (UHE) cosmic rays, atomic nuclei that slam into the atmosphere at colossal speed. Researchers want to pinpoint their sources, but because the nuclei are charged, magnetic fields in space bend their paths, obscuring their origins. But theorists believe that as UHE cosmic rays set out from their sources, they spawn so-called cosmogenic neutrinos in collisions with photons and, because neutrinos are not charged, they travel to Earth as straight as an arrow. The hard part is catching them.