For the first time, researchers reveal the origin of neutrinos, elementary particles that reach our planet from the depths of the Universe.
Highly energetic and difficult to detect, neutrinos travel billions of light years before reaching Earth. Although it is known that these elementary particles come from the depths of our Universe, their precise origin is still a mystery. An international research team, led by the University of Würzburg and the University of Geneva (UNIGE), is shedding light on one aspect of this enigma: neutrinos are thought to be born in blazars, galactic nuclei fed by supermassive black holes. These results were published on July 14 in the journal Astrophysical Journal Letters.
Our planet’s atmosphere is continuously bombarded by cosmic rays. These consist of electrically charged particles of extremely high energies — up to 1020 electron volts. For reference, that is a million times more than the energy achieved in the world’s most powerful particle accelerator,
Following this first encouraging step, in June 2021 Prof. Buson’s group began an ambitious multi-messenger research project with the support of the European Research Council. This involves analyzing various signals (“messengers,” e.g. neutrinos) from the Universe. The main goal is to shed light on the origin of astrophysical neutrinos and possibly establish blazars as the first source of extragalactic high-energy neutrinos with high certainty.
The project is now showing its first success: In the journal Astrophysical Journal Letters, Sara Buson, along with her group, the former postdoctoral researcher Raniere de Menezes (JMU) and Andrea Tramacere from the University of Geneva, reports that blazars can be confidently associated with astrophysical neutrinos at an unprecedented degree of certainty.
Revealing the role of blazars
Andrea Tramacere is one of the experts in numerical modeling of acceleration processes and radiation mechanisms acting in relativistic jets — outflows of accelerated matter, approaching the speed of light — in particular blazar jets. “The accretion process and the rotation of the
Despite this success, the research team believes that this first sample of objects is only the ‘tip of the iceberg’. This work has enabled them to gather “new observational evidence”, which is the most important ingredient for building more realistic models of astrophysical accelerators. “What we need to do now is to understand what the main difference is between objects that emit neutrinos and those that do not. This will help us to understand the extent to which the environment and the accelerator ‘talk’ to each other. We will then be able to rule out some models, improve the predictive power of others and, finally, add more pieces to the eternal puzzle of cosmic ray acceleration!”
Reference: “Beginning a Journey Across the Universe: The Discovery of Extragalactic Neutrino Factories” by Sara Buson, Andrea Tramacere, Leonard Pfeiffer, Lenz Oswald, Raniere de Menezes, Alessandra Azzollini and Marco Ajello, 14 July 2022, Astrophysical Journal Letters.
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