When the sun was young and faint and the Earth was barely formed, a gigantic black hole in a distant galaxy spat out a powerful jet of radiation. That jet contained neutrinos — subatomic particles so tiny and difficult to detect that they are nicknamed “ghost particles.”
Four billion years later, at Earth’s South Pole, 5,160 sensors buried more than a mile beneath the ice detected a single ghostly neutrino. Scientists then traced the particle back to the galaxy that created it.
The cosmic achievement, reported by a team of more than 1,000 researchers in the journal Science, is the first time that scientists have detected a high-energy neutrino and been able to pinpoint where it came from. It heralds the arrival of a new era of astronomy in which researchers can learn about the universe using neutrinos as well as ordinary light.
This is physics at its most mind-boggling and extreme. Researchers compared the breakthrough to the 2017 detection of ripples in space time caused by colliding dead stars.
Neutrinos are so small that they seldom bump into atoms so humans can’t feel them. They don’t shed light, so our eyes can’t see them. Yet these very qualities make them invaluable for conveying information across time and space, scientists say. Light can be blocked and gravitational waves can be bent, but neutrinos are unscathed as they travel from the most violent events in the universe into a detector at the bottom of the Earth.
Scientists call the kinds of signals they can detect through space, like radio waves or gravitational waves or now neutrinos, “messengers.” If you’re trying to understand chaotic phenomena happening billions of light-years away, it’s helpful to have a messenger like a neutrino: one that doesn’t get lost.
Neutrinos arrive on Earth at varying energy levels, which are signatures of the processes that created them. By pairing neutrino detections with light observations, said particle physicist Heidi Schellman, who was not involved with the research, scientists will be able to answer questions about distant cataclysms, test theories about the composition of the universe, and refine their understanding of the rules of physics.
This high-energy neutrino was created in the fast-moving swirl of matter around a supermassive black hole at the center of the galaxy. When this black hole generates a jet of radiation, and that jet is aimed at Earth, scientists call the galaxy a “blazar.” Analysis revealed that this blazar had also produced a flare of more than a dozen neutrino events several years earlier.
The discovery, from the neutrino detector called IceCube, has also solved a mystery that stumped scientists for generations: What is the source of mysterious cosmic rays? These energetic particles have been detected raining down from space since 1912, but researchers could not figure out what phenomenon could produce them.
Astroparticle physicist and IceCube spokesman Darren Grant said it’s as though scientists have spent 100 years listening to thunder with their eyes closed and never known what caused the booming sound. It wasn’t until they looked up and saw lightning that it made sense. Both sound and light — or in this case, cosmic rays and neutrinos — are coming from the same event. “That’s why this is exciting,” Grant said. “It’s a brand new vision on what’s happening in the universe.”