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Where neutrinos come from

Russian version

Russian researchers trace high-energy neutrino origins to black holes in far-off quasars

Russian astrophysicists have come close to solving the mystery of where high-energy neutrinos come from in space. The team compared the data on the elusive particles gathered by the Antarctic neutrino observatory IceCube and measured with radio telescopes in the long electromagnetic waves. Cosmic neutrinos turned out to be linked to flares at the centers of distant active galaxies (quasars), which are believed to host supermassive black holes. As matter falls toward the black hole, some of it is accelerated and ejected into space, giving rise to neutrinos that then coast through the Universe at nearly the speed of light.

The result has been obtained thanks to the long-term measurements of more than one thousand quasars with the RATAN-600 radio telescope (the Special Astrophysical Observatory of the Russian Academy of Sciences). The RATAN-600 is one of the largest radio telescopes in the world. Due to its possibility to record quasi-simultaneous radio spectra at different radio frequencies, a unique experimental material has been obtained which allows establishing a connection between the ultra-high energy cosmic neutrinos (200 trillion electron volts or more) and quasars' flare activity. The observational data have been analyzed by the astrophysicists of the Lebedev Physical Institute of RAS, the Moscow Institute of Physics and Technology and the Institute for Nuclear Research of RAS.

The study is published in the The Astrophysical Journal and is also available from the arXiv preprint repository. The scientists revealed that the areas where high-energy neutrinos come from coincide with the locations of bright quasars.

The elusive particles have been found to emerge during radio flares at the centers of quasars.

"Previous research on high-energy neutrino origins had sought their source right 'under the spotlight'. We thought we would test an unconventional idea, with little hope of success. But we got lucky!" Yuri Kovalev from the Lebedev Institute commented.

Neutrinos are mysterious particles so tiny that researchers do not even know their mass. They pass effortlessly through objects, people, and the entire Earth. The principle of the IceCube observatory operation is based on this neutrino property – only neutrinos can pass through the Earth. High-energy neutrinos are created when protons accelerate to nearly the speed of light. TheĀ IceCube observatory detects such neutrinos and estimates their energy and incoming direction.

The detection of ultra-high energy neutrinos coming from quasars opens a new stage of multi-messenger astronomy and confirms the idea that quasars are potential sources of these particles. Studying electromagnetic radiation, gravitational waves, and elementary particles comprehensively, multi-messenger astronomy is one of the most topical areas of up-to-date astrophysical research. At present, the intensity of quasar observations with RATAN-600 have increased, as it became clear it could be a key to the nature of neutrinos. Due to the new IceCube neutrino detections in 2020, the observations and analysis of such events with RATAN-600 are ongoing.

Alexander Plavin, Yuri Y. Kovalev, Yuri A. Kovalev, Sergey Troitsky, Observational Evidence for the Origin of High-energy Neutrinos in Parsec-scale Nuclei of Radio-bright Active Galaxies, 2020, The Astrophysical Journal, Volume 894, Number 2

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The Russian RATAN-600 telescope helps to understand the origin of cosmic neutrinos. Illustration by Daria Sokol, MIPT ©