GENEVA — An international observatory has for the first time traced a high-energy cosmic neutrino — an invisible, nearly massless subatomic particle — back to its origin in a distant galaxy about 4 billion light years away.
The neutrino was detected by a team of scientists working in the IceCube Neutrino Observatory built at the U.S.-operated Amundsen–Scott South Pole Station, where 5,200 sensors are buried a mile beneath the ice to find high-energy cosmic neutrinos.
They are so hard to detect that scientists refer to them as “ghostly” subatomic particles. Neutrinos travel to Earth unhindered for billions of light years, from the most extreme environments in the universe.
The discovery, announced on July 12 based on evidence published in two articles in Science, marks the first time that scientists have matched a neutrino with its source. That could unlock a deeper understanding of some of the fundamental rules of physics.
The observations, confirmed by telescopes around the globe and in Earth’s orbit, will “help resolve a more than a century-old riddle about what sends subatomic particles such as neutrinos and cosmic rays speeding through the universe,” the observatory said in a statement.
Earlier this year, the European Organization for Nuclear Research, known by its French acronym CERN, was outfitting its Large Hadron Collider — the world’s biggest atom smasher — to operate in a high-luminosity mode from 2026 on.
Luminosity refers to the number of collisions among sub-atomic particles. The higher the luminosity, the more data becomes available. The upgrades will increase the number of proton collisions for experiments.
By accelerating particles to near the speed of light and smashing them together, particle colliders help to discover new elementary particles. The upgrade to the LHC is meant to boost the probability of more discoveries about the universe’s fundamental properties.
The LHC was designed to push bunches of protons in opposite directions at close to the speed of light so that they collide at four points. The aim is to recreate conditions a split second after the Big Bang, which scientists theorize was the massive explosion that created the universe.
During its first run, the LHC was used to discover in 2012 the subatomic particle known as the Higgs boson — commonly referred to in non-scientific circles as the “God particle” — without which particles would not hold together and there would be no matter.
We caught it! NSF’s @uw_icecube catches first high-energy neutrino in the Antarctic ice and telescopes around the world confirmed it. https://t.co/fP1GDgnvAd #BlazarNeutrino pic.twitter.com/5nXdNw65YH
— National Science Foundation (@NSF) July 12, 2018
The IceCube Collaboration
Some 300 physicists, computer scientists and engineers from 49 institutions in at least a dozen countries make up the IceCube Collaboration, which uses the South Pole observatory to detect several hundred neutrinos every day that are produced near Earth.
The observatory, however, detected a neutrino that was very different from the others on September 22, 2017. It had far more energy, and turned out to have come from a supermassive black hole at the center of a galaxy 4 billion light years from Earth.
Cosmic rays are charged particles, so their paths cannot be traced directly back to their sources due to the powerful magnetic fields that fill space and warp their trajectories, the U.S. National Science Foundation-supported observatory said.
But the neutrino was traced back to a blazar, a galaxy with a supermassive black hole at its center, which serves as a powerful cosmic accelerator. Astronomers designated the blazar as TXS 0506+056. About 20 observatories on Earth and in space participated in the identification of what scientists described as a source of very high energy neutrinos and, thus, of cosmic rays.
“The evidence for the observation of the first known source of high-energy neutrinos and cosmic rays is compelling,” says Francis Halzen, a University of Wisconsin–Madison professor of physics and lead scientist for the IceCube Neutrino Observatory.
NSF Director France Anne-Dominic Córdova said the discovery signifies the arrival of an era of “multi-messenger astrophysics” — coordinated observation and interpretation of different signals from space.
“Each messenger — from electromagnetic radiation, gravitational waves and now neutrinos — gives us a more complete understanding of the universe, and important new insights into the most powerful objects and events in the sky,” she said. “Such breakthroughs are only possible through a long-term commitment to fundamental research and investment in superb research facilities.”