Cosmic rays that consist of highly energized electrically charged particles continuously bombard the earth’s atmosphere. These particles come from deep outer space, they have traveled billions of light years. However, Where do they originate? What shoots them through the Universe with such tremendous force? These questions have been among the most significant challenges of astrophysics for over a century.
An international research team led by the University of Würzburg and the University of Geneva (UNIGE) is shedding light on one aspect of this mystery: neutrinos are thought to be born in blazars, galactic nuclei fed by supermassive black holes.
Sara Buson has always thought of it as a significant task. In 2017, the researcher and his associates introduced a blazar (TXS 0506+056) as a potential neutrino source for the first time. That study sparked a scientific debate about whether there truly is a connection between blazars and high-energy neutrinos.
After taking this initial, positive step, Prof. Buson’s team received funding from the European Research Council to launch an ambitious multi-messenger research project in June 2021. Analyzing numerous signals (or “messengers,” for example, neutrinos) from the Universe is required. The primary objective is to shed light on the origin of astrophysical neutrinos, potentially confirming blazars as the first highly certain source of high-energy extragalactic neutrinos.
The project is now showing its first success. Scientists confirm- blazars can be confidently associated with astrophysical neutrinos at an unprecedented degree of certainty.
Andrea Tramacere from the University of Geneva said, “The accretion process and the rotation of the black hole lead to the formation of relativistic jets, where particles are accelerated and emit radiation up to energies of a thousand billion of that of visible light! The discovery of the connection between these objects and the cosmic rays may be the ‘Rosetta stone’ of high-energy astrophysics!”
Scientists used neutrino data from the IceCube Neutrino Observatory in Antarctica and BZCat, one of the most accurate catalogs of blazars. Using this data, they had to prove that the blazars whose directional positions coincided with those of the neutrinos were not there by chance.
Scientists then develop software that can estimate how much the distributions of these objects in the sky look the same.
Andrea Tramacere said, “After rolling the dice several times, we discovered that the random association could only exceed that of the real data once in a million trials! This is strong evidence that our associations are correct.”
Despite their achievement, the study team feels that the number of things in this initial sample is just the “tip of the iceberg.” They have collected “new observational evidence” thanks to their effort, which is the key component in creating more accurate models of astrophysical accelerators.
Scientists noted, “What we need to do now is to understand the main difference 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!”
- Sara Buson, Andrea Tramacere, et al. Beginning a Journey Across the Universe: The Discovery of Extragalactic Neutrino Factories. Published 2022 July 14 • © 2022. The Author(s). Published by the American Astronomical Society. DOI: 10.3847/2041-8213/ac7d5b