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Researchers hope to use neutrinos to find the sources of cosmic radiation. New algorithms out of Bochum are aiding in the search, and have also eliminated a few candidates.

Since 2009, an international research team has been using the IceCube neutrino detector at the South Pole to search for the source of cosmic radiation. New algorithms developed by the Bochum-based group of Professor Anna Franckowiak increase the likelihood of discovery.

With these algorithms, the energy and direction of the particles measured by IceCube can be determined in real time, allowing telescopes around the world to search for the origins of the particles. The team is also using the new algorithms to re-evaluate archived data, and recently had to reject several candidates for the sources of cosmic rays.

Three publications have come out of this research. is published in The Astrophysical Journal and are posted to the arXiv preprint server.

Cosmic radiation continuously bombards Earth in the form of various particles such as electrons, protons, and neutrinos, yet their origin is unknown. Neutrinos can penetrate space and matter over vast distances without interacting. This makes them ideal candidates for searching for the sources of cosmic radiation because they travel a more or less direct path from their source to Earth. There, they can be detected by IceCube.

Quickly and precisely determining neutrino trajectories

Anna Franckowiak's team's algorithm for analyzing neutrino trajectories works with speed and precision. "We need 30 seconds to calculate the energy and direction of a neutrino, and immediately disseminate the information worldwide," explains Franckowiak, lead of the Research Group for Multi-wavelength and Multi-messenger Astronomy. She is also a member of the Collaborative Research Center "Cosmic Interacting Matter," coordinated in Bochum.

The team then uses a slower algorithm to refine the first, instant result and updates the original neutrino information. Calculation of the trajectory is now four to five times more precise than with previous methods.

Telescopes around the world use the neutrino alerts to scour the region of the sky that the neutrino came from to search for any particularly energy-rich objects that could have emitted the particle. "These celestial objects might only light up very briefly, so it's crucial that our system works in real time," says Franckowiak.

Still no sources

Once a potential source for the neutrino has been found, the calculations resume. "Then we determine how likely it is that, when we look in the direction the neutrino came from, we see such a celestial object light up that has nothing to do with the neutrino," Franckowiak explains.

The researchers had considered tidal disruption events as emitters of neutrinos. "These occur when a star comes too close to an inactive black hole that is not swallowing up any matter, but stretches the star because of its strong gravity. The side of the star facing the black hole is pulled further than the other side, which can tear the star apart," says the physicist.

Over the years, IceCube had discovered three neutrino events that may have been attributable to tidal disruption events. However, "After we improved our algorithm for trajectory reconstruction, we analyzed the events again and the neutrino paths don't match the positions where the tidal disruption events occurred," says Franckowiak.