Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Highest-energy cosmic rays have extragalactic origin

25.09.2017

Cosmic rays are atomic nuclei that travel through space at speeds close to that of light. Low-energy cosmic rays come from the Sun or from our own Galaxy, but the origin of the highest-energy particles has been the subject of debate ever since they were first discovered fifty years ago: do they come from our Galaxy or from distant extragalactic objects?

The question has now been settled by studying 30 000 cosmic-ray particles with energies a million times greater than those of the protons accelerated in the LHC . They were detected from 2004 to 2016 at the largest cosmic ray observatory ever built, the Pierre Auger Observatory in Argentina.


The detectors are tanks filled with 12 tonnes of pure water, which are used to detect particles from air showers, cascades of secondary particles produced when cosmic rays enter Earth's atmosphere. As they travel through the tanks of water, the secondary particles produce a flash of light caused by the Cherenkov effect. The Pierre Auger Observatory in Argentina is the world's largest cosmic ray detector. It is named after the French physicist who was the first to observe air showers, in 1938.

Credit: Céline ANAYA-GAUTIER/CNRS Photothèque

Analysis of the arrival directions of the particles showed that at such energies the flux of cosmic rays coming from a region of the sky located 120 degrees from the galactic center is approximately 6% higher than if the flux were perfectly uniform.

This direction cannot be associated with potential sources in either the galactic plane or galactic center, providing the first convincing evidence that these cosmic rays have an extragalactic origin.

The flux of these very high-energy cosmic rays (exceeding 2 joules) is about one particle per square kilometer per year . When the cosmic rays collide with molecules in the upper atmosphere, they create cascades of over 10 billion secondary particles, known as air showers, which can cover an area exceeding 40 square kilometers by the time they reach the ground.

The Pierre Auger Observatory detects some of these secondary particles (electrons, photons and muons) by means of an array of 1 600 detectors, i.e. tanks of pure water spaced 1.5 kilometers apart and covering 3 000 square kilometers in the Argentinian pampas, an area slightly larger than Luxembourg. By comparing the arrival times of particles at the different detectors it is possible to determine where the cosmic ray particle that produced the air shower came from.

This discovery clearly indicates an extragalactic origin for these cosmic rays, since there is a probability of only one in five million that the pattern observed in the sky is due to chance. However, the study has not yet succeeded in locating the sources precisely. This is because the region where cosmic rays are brightest covers a large part of the sky, where the number of galaxies is relatively high. In addition, our Galaxy's magnetic field deflects the paths of these charged particles , making it more difficult to locate their sources.

Some cosmic rays have even higher energies than those focused on in this survey. They have the disadvantage of being even more unusual, but also the advantage that they are not as deflected by the magnetic field of our own Galaxy. Their direction of arrival may therefore more accurately indicate the region where they were produced.

In 2007, an earlier study pointed to a correlation between active galactic nuclei and the arrival directions of the highest-energy cosmic rays then detected , but this correlation subsequently turned out to be not very significant. Research is currently being carried out on a much larger sample of ultrahigh-energy cosmic rays, and may provide some answers. At the same time, an upgrade program is underway at the Pierre Auger Observatory, which should make it easier to identify the sources.

400 scientists from 18 countries take part in the Pierre Auger Collaboration, which develops and runs the observatory of the same name. The CNRS is the observatory's principal French funding agency. The following French laboratories contribute to the collaboration:

  • the Institut de Physique Nucléaire d'Orsay (CNRS/Université Paris-Sud) ;
  • the Laboratoire de Physique Nucléaire et des Hautes Energies (CNRS/UPMC/Université Paris Diderot) ;
  • the Laboratoire de Physique Subatomique et de Cosmologie (CNRS/Université Grenoble Alpes/ Grenoble INP).

Media Contact

Veronique Etienne
veronique.etienne@cnrs.fr
33-144-965-137

http://www.cnrs.fr 

Veronique Etienne | EurekAlert!

More articles from Physics and Astronomy:

nachricht The cascade to criticality
02.06.2020 | ETH Zurich Department of Physics

nachricht K-State study reveals asymmetry in spin directions of galaxies
02.06.2020 | Kansas State University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New measurement exacerbates old problem

Two prominent X-ray emission lines of highly charged iron have puzzled astrophysicists for decades: their measured and calculated brightness ratios always disagree. This hinders good determinations of plasma temperatures and densities. New, careful high-precision measurements, together with top-level calculations now exclude all hitherto proposed explanations for this discrepancy, and thus deepen the problem.

Hot astrophysical plasmas fill the intergalactic space, and brightly shine in stellar coronae, active galactic nuclei, and supernova remnants. They contain...

Im Focus: Biotechnology: Triggered by light, a novel way to switch on an enzyme

In living cells, enzymes drive biochemical metabolic processes enabling reactions to take place efficiently. It is this very ability which allows them to be used as catalysts in biotechnology, for example to create chemical products such as pharmaceutics. Researchers now identified an enzyme that, when illuminated with blue light, becomes catalytically active and initiates a reaction that was previously unknown in enzymatics. The study was published in "Nature Communications".

Enzymes: they are the central drivers for biochemical metabolic processes in every living cell, enabling reactions to take place efficiently. It is this very...

Im Focus: New double-contrast technique picks up small tumors on MRI

Early detection of tumors is extremely important in treating cancer. A new technique developed by researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from normal tissue. The work is published May 25 in the journal Nature Nanotechnology.

researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from...

Im Focus: I-call - When microimplants communicate with each other / Innovation driver digitization - "Smart Health“

Microelectronics as a key technology enables numerous innovations in the field of intelligent medical technology. The Fraunhofer Institute for Biomedical Engineering IBMT coordinates the BMBF cooperative project "I-call" realizing the first electronic system for ultrasound-based, safe and interference-resistant data transmission between implants in the human body.

When microelectronic systems are used for medical applications, they have to meet high requirements in terms of biocompatibility, reliability, energy...

Im Focus: When predictions of theoretical chemists become reality

Thomas Heine, Professor of Theoretical Chemistry at TU Dresden, together with his team, first predicted a topological 2D polymer in 2019. Only one year later, an international team led by Italian researchers was able to synthesize these materials and experimentally prove their topological properties. For the renowned journal Nature Materials, this was the occasion to invite Thomas Heine to a News and Views article, which was published this week. Under the title "Making 2D Topological Polymers a reality" Prof. Heine describes how his theory became a reality.

Ultrathin materials are extremely interesting as building blocks for next generation nano electronic devices, as it is much easier to make circuits and other...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Dresden Nexus Conference 2020: Same Time, Virtual Format, Registration Opened

19.05.2020 | Event News

Aachen Machine Tool Colloquium AWK'21 will take place on June 10 and 11, 2021

07.04.2020 | Event News

International Coral Reef Symposium in Bremen Postponed by a Year

06.04.2020 | Event News

 
Latest News

Perfect optics through light scattering

02.06.2020 | Power and Electrical Engineering

The digital construction site: A smarter way of building with mobile robots

02.06.2020 | Architecture and Construction

Process behind the organ-specific elimination of chromosomes in plants unveiled

02.06.2020 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>