Claudio Kopper didn’t think there was anything to see in that part of the sky, but he was wrong. What he and other scientists around the world soon observed on Earth and in space marked the beginning of a new age of astrophysics — one in which a long-elusive “ghost particle,” or high-energy neutrino, can finally be traced back to its mysterious origins.
Optical detectors at the IceCube Neutrino Observatory in Antarctica picked up evidence of a high-energy neutrino in September 2017, prompting the project’s computers to begin calculating where in the universe the particle may have come from. Neutrinos are tiny subatomic particles with so little mass they barely interact with anything in space, making it incredibly difficult for physicists like the University of Alberta’s Kopper, an assistant professor of physics, and his hundreds of collaborators to study them and trace their origins.
With the new data, which are described Thursday in a groundbreaking pair of Science papers, IceCube collaborators alerted other laboratories around the world to gaze at that part of the sky and figure out what emitted the neutrino.
Against all odds, they succeeded.
Together, these papers support the idea that blazars are a source of the cosmic rays that create the evasive ghost particles. Neutrinos are produced when the high-energy protons and atomic nuclei in cosmic rays smash together, so where there are neutrinos, there are cosmic rays.