Scientists reveal for the first time the origin of neutrinos

Cosmic rays consisting of electrically charged particles of high energy are constantly bombarding the Earth’s atmosphere. These particles come from deep space, they have traveled billions of light years. However, where did they come from? What shot them through the Universe with such incredible power? These questions have been one of the most significant challenges of astrophysics for more than a century.

An international team of researchers led by the University of Würzburg and the University of Geneva (UNIGE) sheds light on one aspect of this mystery: neutrinos are thought to have been born in a blazar, the core of a galaxy that is fed by a supermassive black hole.

Sara Buson has always considered it a significant task. In 2017, researchers and their colleagues introduced blazar (TXS 0506+056) as a potential neutrino source for the first time. The study sparked a scientific debate about whether there really is a link between blazars and high-energy neutrinos.

After taking this positive initial step, Prof. Buson received funding from the European Research Council to launch an ambitious multi-messenger research project in June 2021. Analyzing the multiple signals (or “messengers”, for example, neutrinos) from the Universe is what is needed. The ultimate goal is to elucidate the origin of astrophysical neutrinos, potentially confirming blazars as the first very definite source of extragalactic high-energy neutrinos.

The project is now showing its first success. Scientists confirm that blazars can be confidently associated with astrophysical neutrinos with an unprecedented degree of certainty.

Andrea Tramacere of the University of Geneva said, “The process of accretion and rotation of black holes leads to the formation of relativistic radiance, in which particles are accelerated and emit radiation of up to a thousand billion energies of visible light! The discovery of the connection between these objects and cosmic rays may be the ‘Rosetta stone’ of high energy astrophysics!”

The scientists used neutrino data from the IceCube Neutrino Observatory in Antarctica and BZCat, one of the most accurate blazar catalogs. Using this data, they had to prove that a blazar whose direction coincided with that of a neutrino didn’t exist by chance.

Scientists then developed software that could estimate how much the distribution of these objects in the sky looked the same.

Andrea Tramacere says, “After rolling the dice several times, we discovered that random associations could only exceed real data once in a million trials! This is strong evidence that our association is correct.”

Despite their achievements, the study team felt that the number of things in this initial sample was just the “tip of the iceberg.” They have accumulated “new observational evidence” thanks to their efforts, which is a key component in creating more accurate astrophysical accelerator models.

The scientists noted, “What we need to do now is understand the main difference between objects that emit neutrinos and those that don’t. This will help us understand the extent to which the environment and the accelerator ‘talk’ to each other. We’ll then be able to override some models, increase the predictive power of others and, finally, add more pieces to the eternal puzzle of cosmic ray acceleration!

Journal Reference:

1. Sara Buson, Andrea Tramacere, et al. Embark on a Journey through the Universe: The Discovery of the Extragalactic Neutrino Factory. Published 2022 July 14 • © 2022. Author. Published by the American Astronomical Society. DOI: 10.3847/2041-8213/ac7d5b

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