Gravitational waves have deservedly held the astronomical spotlight for the last two years, opening up a new way to see the cosmos. But thanks to a groundbreaking discovery, it might well be time for the humble neutrino to take the stage.
That’s because, for the first time ever, a global team of astronomers has found the source of some of these high-energy particles coming from the distant universe. Neutrinos are hard to spot, and we've never found the source of any at such a distance before.
But in two papers in the journal Science, scientists describe how they located a source of neutrinos 4 billion light-years from Earth. It’s an energetic galaxy known as a blazar, called TXS 0506+056, which has a giant spinning supermassive black hole at its core and fires out twin jets of particles.
On September 22, 2017, the IceCube observatory at the South Pole detected an incoming high-energy neutrino. This advanced detector has a real-time alert system, and broadcasted the coordinates of the detection to astronomers around the world just 43 seconds after its discovery.
About 20 observatories including NASA's orbiting Fermi Gamma-ray Space Telescope responded to the alert, and trained their views on the skies to try to work out where it was coming from. What they found was this blazar, energetically flaring and sending out gamma rays. And, as luck would have it, it also sent neutrinos in our direction, and we were able to detect one.
“These results are a remarkable chain of events,” Darren Grant from the University of Alberta, and spokesperson for IceCube, told IFLScience. “Taken all together, these results provide an incredibly intriguing picture for the first identified cosmic ray source.”
Looking through the archives of IceCube’s data, scientists found a further dozen events associated with this object in late 2014 and early 2015. That helped them confirm that the single high-energy neutrino spotted in 2017 almost certainly came from the blazar.
And that’s important for a number of reasons. For one, it’s the first time we’ve ever found the source of a high-energy neutrino. For another, it’s the most distant detection of a neutrino in the universe we’ve ever made. And it tells us a lot more about cosmic rays.