For more than a century the source of cosmic rays has been a mystery. We know they continuously rain down on Earth from space, but we’ve never been quite sure where they’re coming from. As cosmic rays are charged particles, their trajectories get altered by magnetic fields in space, making it hard to see where they’re coming from.
Neutrinos, however, act as “ghost particles” – as they have almost no mass and rarely interact with matter. So neutrinos from this blazar traveled in almost a straight line directly towards Earth, allowing their origin to be worked out.
On two previous occasions we have detected sources of low-energy particles associated with cosmic rays, namely the Sun and a nearby supernova, called SN 1987A. High-energy neutrinos, however, can tell us a whole lot more about how fascinating objects like blazars actually work.
“We are at the beginning of understanding what sources and mechanisms can accelerate these tiny particles to such high energies,” Azadeh Keivani from Penn State University told IFLScience. “The discovery of high-energy neutrino sources could tell us about the origins of cosmic rays that produce them in particle interactions at the source.”
The discovery of gravitational waves meant that we could study some extreme events in the universe, like merging black holes and neutron stars, which are impossible to see with regular telescopes. In a similar manner, high-energy neutrinos allow us to see another hidden side of the universe.
By observing events in both light and neutrinos, this opens up a new type of multimessenger astronomy. This can tell us more about how distant galaxies form and evolve, and probe some of the processes taking place in things like supermassive black holes.
“Blazars dominate the high-energy sky and therefore they have long been proposed as potential neutrino sources,” Dr Marcos Santander from the University of Alabama told IFLScience. “We need to understand what could make TXS 0506+056 a neutrino source in order to find more like it among the thousands of blazars known to emit gamma rays.”
To make more detections like this in future, scientists are already working to upgrade IceCube, tentatively calling it IceCube-Gen2, to increase its volume by 10 times. Coupled with upcoming gamma-ray observatories like the Cherenkov Telescope Array, scientists hope to be able to pinpoint even more neutrino sources.
Along with the discovery of gravitational waves, it heralds an exciting new era of astronomy where we can study objects not just in electromagnetic radiation, but in the other particles they emit too. Before we could see the universe – now we can hear it, too.