Light, and all other forms of electromagnetic radiation, have been the traditional messenger of things outside our galaxy. The particles of light (photons) collected by massive telescopes on the ground and in space have had a rough journey to get here. From being produced in distant stars and galaxies, they have been constantly bumped around by the electric and magnetic fields of other stars and galaxies. Some are hassled so much they don’t make it to us, reducing the apparent brightness we see. Some are just bent in large groups so that we might think them coming from another point in the sky.
Ice Cube does not collect particles of light but instead looks at neutrinos. With no electric charge, neutrino particles are not bumped around on their journey to us from the deepest reaches of the universe. They instead fly straight and true, which means that they show a true brightness and position in the night sky of whatever created them.
Without an electric charge it is very difficult to catch a neutrino. Right now over 200 billion are streaming through your body each second, yet over your entire lifetime you’d be lucky if even one noticed you existed. So Ice Cube, and other neutrino experiments, don’t really collect neutrinos but instead sample about one in every billion trillion that might pass through. With these odds it makes astronomy with neutrinos difficult but Ice Cube have proven it is not impossible.
The results from the experiment show that they have seen an excess of ultra-high-energy neutrinos in the massive kilometre-cubed detector. With just a handful of sightings it is still not clear that any two of the neutrinos have come from the same source. Nonetheless, with energies over 100 times that seen in the Large Hadron Collider they are thought to have to come from the most massive things in the universe, such as super-massive black holes.
Neutrino astronomy requires patience, but it is beginning to pay off. We have gone beyond the electromagnetic spectrum, and, with this new perspective, we hope to go beyond our current understanding of nature. This is the start. What we will learn has yet to be written.
1 The Ice Cube Neutrino Observatory in Antarctica. Credit: Sven Lindstrom/National Science Foundation
2 A neutrino splashing down in the kilometre cubed Ice Cube experiment. The light from the neutrino interaction is collected by the electronics and the energy and direction of the neutrinos travel is reconstructed.
3 The distribution in the sky of the sources of the high energy neutrinos. The cluster on the left has an 8% probability of happening through random chance and is therefore not significant enough to say that the neutrinos seen there have come from a single source.