Scientists for the first time have been able to pinpoint the source of an extremely powerful version of a neutrino, a ghostly particle that can travel virtually unimpeded through space.
It's an achievement that opens a whole new way of looking at the universe.
The neutrino was detected by a South Pole observatory called IceCube that was specifically designed to catch the particles. It consists of a cubic kilometer of ice festooned with more than 5,000 detectors.
Neutrinos don't interact with much, but occasionally one will strike another particle, giving off a kind of light known as Cherenkov radiation that IceCube's detectors can pick up.
When a particularly high-energy neutrino is captured, IceCube sends out an alert.
"We had this neutrino alert in September 2017," says Olga Botner, a particle physicist at Uppsala University in Sweden and a member of the IceCube scientific team. On Sept. 22, to be precise.
When the alert went out, a bevy of observatories on Earth and in space started searching the portion of the sky where the neutrino appeared to be coming from, looking for something that might have generated it.