📰 Neutrino factories in deep space

An international research team reveals for the first time the origin of neutrinos, elementary particles that reach our planet from the depths of the universe.

Artist’s impression of a blazar that accelerates cosmic rays, neutrinos, and photons, as seen in the PeVatron blazars.
© Benjamin Amend

Highly energetic and difficult to detect, neutrinos travel billions of light years before reaching ours planet (A planet is a celestial body that orbits the Sun or another star in…). If we know that these elementary particles come from the depths of our Universe (The universe is the sum of everything that exists and the laws that govern it.), their precise origin remains unknown. An international team of research (Scientific research initially refers to all measures undertaken with a view to…) driven byUniversity (A university is an institution of higher education whose aim is…) of Würtzburg (JMU) in Germany andUniversity of Geneva (The University of Geneva (UNIGE) is the public university in the canton of Geneva in…) (UNIGE), unravels part of this mystery: neutrinos would especially be born in blazars, galactic nuclei fed by supermassive black holes. These results are to be discovered in the journal Astrophysical Journal Letters.

L’earth’s atmosphere (Earth’s atmosphere is the gaseous mantle that surrounds the solid earth. Dry air consists of…) is continuously bombarded with cosmic rays. These consist of electrically charged particles, theenergy (In common sense, energy refers to anything that allows you to do work, make energy, etc.) can reach 1020 electron-volts. It is a million (One million (1,000,000) is the natural number after nine hundred and ninety-nine…) times more than the energy reached inparticle accelerator (Particle accelerators are instruments that use fields…) the most powerful of world (The word world can refer to:)large collides (A collider is a type of particle accelerator that involves beams…) of Hadrons from CERN, Geneva. These extremely energetic particles come from deep space. They thus traveled billions of light years before reaching our planet. Where exactly do they come from and what drives them into the universe with such strength (The word force can denote a mechanical power over things, and also, metaphorically, a…)? This question has been in more than one century (A century is now a period of one hundred years. The word comes from the Latin saeculum, in, which…) one of the biggest challengesastrophysics (Astrophysics (from Greek astro = star and physiqui = physics) is a branch…).

Cosmic ray birthplaces are known to produce neutrinos, neutral particles that are difficult to detect. Their lot (The term mass is used to denote two quantities linked to a…) is actually almost zero and they hardly interact with fabric (Matter is the substance that makes up any body that has a tangible reality. Its…). They “run” in the universe and can pass through galaxies, planets and human body (The human body is the physical structure of a person.) almost without leaving track (TRACE is a NASA space telescope designed to study the connection between…). “Astrophysical neutrinos are produced exclusively during processes involvingacceleration (Acceleration commonly refers to an increase in speed; in physics,…) cosmic rays,” says Sara Buson, professor of astrophysics at the Julius-Maximilians-Universität (JMU) in Würzburg, Germany. This is precisely what makes neutrinos unique messengers, paving the way for source localization. of cosmic rays.

Towards the end of a controversial debate?

Despite the great amount (The amount is a generic term for metrology (account, amount); a scalar,…) of data (In information technology (IT), data is an elementary description, often…) collected by astrophysicists on the subject, the connection between high-energy neutrinos and the astrophysical sources that produce them remains largely a mystery. It was in 2017, in an article published in the magazine Science (Science (Latin scientia, “knowledge”) is, according to the dictionary…), that Sara Buson and her collaborators first integrated the idea that a blazar (TXS 0506+056) could be a putative source of neutrinos. Blazars are active galactic nuclei powered by supermassive black holes that emit far more radiation (Radiation, synonymous with radiation in physics, denotes the emission process or…) that all their galaxy (Galaxies is a French quarterly about science fiction. With…). This post sparked a debate scientific (A scientist is a person who is dedicated to the study of a science or sciences and who…) on the existence of a real connection between blazars and high-energy neutrinos.

After this encouraging first step, in June 2021 Sara Buson’s group launched an ambitious project (A project is an irreversible commitment of uncertain outcome, not reproducible to…) study with support from the European Research Council. It consists of analyzing various signals (or “messengers”, such as neutrinos for example) coming from the universe. The main purpose is to make light (Light is the set of electromagnetic waves visible to the eye…) on the origin of neutrinos, possibly establishing with high certainty that blazars are the primary source of high-energy extragalactic neutrinos.

The project is now enjoying its first success: in the Astrophysical Journal Letters, Sara Buson, with her group consisting of former postdoctoral student Raniere de Menezes (JMU) and Andrea Tramacere, seeking (A researcher (fem. researcher) refers to a person whose job is to do research…) at the Department ofastronomy (Astronomy is the science of observing the stars, seeking to explain…) from UNIGE, reports that blazars can be linked to astrophysical neutrinos with a degree (The word degree has several meanings, it is used especially in fields…) unprecedented security.

Reveal the role of blazars

Andrea Tramacere is one of the model experts digital (Digital information is information…) acceleration processes and radiation mechanisms operating in relativistic jets – streams of accelerated matter approaching the speed of light (The speed of light in a vacuum, denoted c (for…) – and especially in the jets of the blazars.

“The process ofgrowth (In astrophysics, geology and meteorology, accretion denotes the increase with…) and the rotation of black hole (In astrophysics, a black hole is a massive object whose gravitational field is so intense…) lead to the formation of relativistic jets, where particles are accelerated and emit radiation up to energies of a trillion times greater than visible light! The discovery of the connection between these objects and cosmic rays could be the “Rosetta stone!” of high-energy astrophysics, explains the UNIGE researcher.

To arrive at these results, the research team overlaid neutrino data obtained by the IceCube Neutrino Observatory of Antarctica (Antarctica (pronounced [ɑ̃.taʁk.tik] Listen) is the most continent…) – that detector (A detector is a technical device (instrument, substance, material) that changes…) most sensitive neutrino array currently in operation – and BZCAT, one of the most accurate catalogs of blazars. “With these data, we had to prove that the blazars, whose directional positions coincided with the position of the neutrinos, were not there chance (In common parlance, the word chance is used to express an effective lack, otherwise…).”

To do this, the UNIGE researcher has developed a software (In computing, software is a set of information related to processing…) can assess how point (graphics) the distribution of these objects in sky (The sky is Earth’s atmosphere as seen from the planet’s ground.) looks like. “After rolling the dice several times, we found that the random association can exceed that of the real data only once in a million trials! This is a strong proof of the correctness of our associations.”

Despite this success, the research team believes that this first sample (Generally, a sample is a small amount of material, information or…) objects are only the “tip of the iceberg”. However, this work allowed him to collect “new observational evidence”, that is, the most important ingredient for building more realistic models of astrophysical accelerators.

“What we need to do now is understand what the main difference is between objects that emit neutrinos and those that don’t. This will help us understand to what extentenvironment (The environment is everything that surrounds us. It is all the natural elements and…) and the accelerator’s ”dialogue”. We will then be able to rule out certain models, improve the predictive power of other models, and finally add new pieces to the eternal puzzle of cosmic ray acceleration!”.

This research is published in Strophysical Journal Letters – ArXiv: https://iopscience.iop.org/article/10.3847/2041-8213/ac7d5b

Andréa Tramacere – Scientific Assistant – Department of Astronomy – Faculty of Science – Andrea.Tramacere@unige.ch

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