Neutrinos in the ice indicate source of cosmic rays
12 July 2018
An international research team that includes researchers from Uppsala University and Stockholm University have identified a likely source for the high energy cosmic rays reaching Earth. The discovery was made with the aid of the IceCube Neutrino Telescope at the South Pole in addition to observations made by about twenty different telescopes around the world.
The results, which were published in two articles in Science on 13 July 2018, mean this is the first time researchers are able to find the likely source for the formation of cosmic rays, something they have been searching for ever since the discovery of cosmic rays in 1912.
It's difficult to observe and measure cosmic rays. The rays consist of charged particles moving through a magnetic field, making it impossible to trace where they come from. Accompanying these rays, however, are neutrinos, elementary particles that have no charge and practically no mass, and that can in principle travel through space without being affected. And it is a neutrino, with an energy of about 300 TeV, which with the aid of the IceCube telescope at the South Pole has been identified and traced back to a likely source – a so-called blazar. A blazar is a giant elliptical galaxy at the centre of which is a massive and fast-spinning black hole. This particular one is named TXS 0506 + 056 and is situated about four billion light years away from the Earth.
“In September of last year IceCube captured an extremely high-energy neutrino which had also alerted other telescopes. At the same time, NASA’s Fermi Satellite and the so-called MAGIC Telescope in the Canary Islands saw an active galaxy flare up several billion light years away in the direction from which the neutrino had come,” says Chad Finley at the Department of Physics at Stockholm University.
Chad Finley has directed the work of analysing previous data from IceCube and has found a dozen or so neutrinos that have come from the same direction. They are further evidence, therefore, that there is a connection between high-energy neutrinos and this active galaxy.
“Blazars – and active galaxies more generally – thus seem to act as the most extreme particle accelerators created by nature,” he says.
What is IceCube?
IceCube is a neutrino telescope embedded a couple of kilometres below the ice at the South Pole and is funded by the National Science Foundation (NSF), a United States federal agency, and also by Germany, Sweden and Belgium as well as seven other countries. The funding from Sweden comes from Swedish Research Council. The collaboration involves 320 researchers from almost fifty institutions around the world. University of Uppsala together with Stockholm University and three other universities, established the first neutrino telescope at the South Pole beginning in 1992.