A team of Antarctic scientists has just verified the existence of cosmic neutrinos — tiny, energetic particles that might hail from far reaches of the Milky Way and beyond. And these ghostly little flecks of matter could hold the key to some of the deepest mysteries of the cosmos.
High-energy cosmic neutrinos are thought to be produced by some of the universe's most violent agents, including black holes, supernovae, and the energetic cores of galaxies. Unchanged as they zip across space and time, these particles may represent something of an intergalactic breadcrumb trail, pointing us in the direction of any number of fascinating astronomical phenomena.
If only we could spot them. That's incredibly tough, because neutrinos contain virtually no mass and no electric charge. And while the common variety of neutrinos — those produced locally — are abundant, interlopers from far away are very, very rare. But in 2013, we got our first strong whiff of the high-energy cosmic particles, when scientists working at the South Pole observed two potential neutrinos, fondly nicknamed "Bert and Ernie." But the matter of Bert and Ernie's distant cosmic origins remained unconfirmed. I mean I believe it, but apparently, it wasn't enough evidence to convince the scientific powers that be.
A study that appears today in Physical Review Letters solidifies the elusive cosmic neutrino's hold on reality. Combing through two years of data collected by thousands of optical sensors sunk deep beneath the ice at the IceCube Neutrino Observatory, researchers identified 21 high-energy muons. These are particles created on the rare occasion that a neutrino slams into something else. The existence of these muons, scientists say, is an "unequivocal signal" that high-energy cosmic neutrinos like Bert and Ernie could have indeed traversed space, unimpeded by planets and even stars.
What's next for cosmic neutrinos? Finding out where they're coming from. When a muon is created, it leaves a trail of light that faithfully mirrors the path of the neutrino. In theory, we can use this cosmic fingerprint to trace the particles to their source. What'll we find when we do? Cthulhu? Sesame Street? A gaping chasm in the fabric of spacetime? The answers are out there.
Picture: One of the highest-energy neutrino events from a survey of the northern sky superimposed on a view of the IceCube Lab at the South Pole, via IceCube Collaboration.