- University
- Research
- Education
- Campus Life
- International
- News
- 2019 News
- Alain Sarfati, elected President of Université Paris-Sud
- A new technique to detect the topography of exoplanets
- Two students from UFR STAPS talk about their study in Russia
- Jean-François Le Gall, winner of the Wolf Prize for Mathematics
- A nanomedicine which relieves pain without the risk of addiction
- Three physicists acknowledged as outstanding referees by the American Physical Society
- Sponsorship agreement with Air Liquide for the Chair in "Another Kind of Physics"
- University Paris-Sud the winner of two European networks for Innovative Training Networks (ITN) doctoral training
- Signature of conventions between the French Anti-Doping Agency and University Paris-Sud
- Kenya: promising partnerships for the future
- Paris-Sud, top French university among the most innovative in Europe
- A student at the Olympics
- Franco-American seminar to boost our university exchanges
- Towards an understanding of the mechanism of transport of membrane lipids
- Paris-Sud University is one of the first 25 institutions accredited with “Choose France” certification
- Paris-Sud University is involved in a European University project along with its partners in the Paris-Saclay COMUE
- GATE is open
- Back to university 2019: welcome to Paris-Sud University!
- Breast Cancer : hormone therapy has a greater impact on quality of life than chemotherapy
- A great Welcome Day for our international students
- Diana Garcià Garcià, winner of the 2019 French Rising Talent Award
- Four researchers from Paris-Sud honored by the Academy of Science
- Graduates of Université Paris-Sud meet-up in Boston
- Publication of the decree creating the Paris-Saclay institution
- 2018 News
- The same fish apart from a few neurons
- Silicon LEDs
- Pulmonary arterial hypertension
- Paris-Sud students excel during a tournament between physicists
- Green light for the ARIEL mission
- Closer co-operation with Japan
- The paradoxical extinction of the most charismatic species
- Planck
- Marc Humbert, Winner of the 2018 European Respiratory Society Prize
- Cachan students shine at the French Robotics Cup
- Studying the magnetic thin layers by analogy with the physics of soap bubbles
- Success Story for the Erasmus Mundus SERP-Chem Masters
- Gene Therapy
- Inauguration of a new biology and health research infrastructure
- Université Paris-Sud is outstanding in the lastest rankings
- Predicting the response to immunotherapy with artificial intelligence
- Pathology and social interactions : Safety in numbers
- Adolescent depression: early signs and changes in brain development underscore the need for new preventive approaches
- Inauguration of International Talents Reception Point
- The Mascot robot successfully lands on its asteroid
- A new international Master's in Life Sciences and Health
- A better understanding of the molecular mechanisms of assembly of some viruses
- Université Paris-Sud warmly welcomed its international students
- Five Researchers from Université Paris-Sud have been honoured by the Academy of Science
- Paris Sud students experience weightlessness
- Four internationally-renowned figures are awarded Doctor Honoris Causa degrees by Université Paris-Sud
- An international programme in English for future sports event managers
- Visit by an American delegation
- The Emerald : a jewell to understand the evolution of early massive galaxies
- Université Paris-Sud will host the French Anti-Doping Agency at its Orsay campus
- HIV : Preventing entry into the cell
- 2017 News
- The Paris-Sud official shop is open
- Paris-Sud University, still among the Top 50 best universities worldwide
- And it was a success... like a flower
- Ultra-Fast Molecular Movie
- Cosmic rays with an extragalactic origin !
- Gravitational waves : fourth merger of black holes observed by LIGO-Virgo
- From Sotchi to the Faculty of Sport Science
- First observation of merging neutron stars
- Antibiotics affects the efficacy of immunotherapy
- Visit by a delegation of 19 representatives from Chinese universities
- Interview of Narendra Singh, our local EIT kickoff winner
- The turbulence of gravitational waves put into an equation
- Rosetta is revealing new secrets about the composition of comet 67P
- The Heating Rate in the Magnetic Environment around the Earth Estimated for the First Time
- 2019 News
- Science and society
Cosmic rays with an extragalactic origin!
It is a 50-year old debate which has now been settled: the highest-energy cosmic rays do not originate from the Milky Way, but have been fired from galaxies located tens, or even hundreds of millions of light-years away. This discovery has just been announced by an international collaboration, including researchers from the Institute of Nuclear Physics at Orsay (CNRS [National Centre for Scientific Research]/Université Paris-Sud).
Cosmic rays are atomic nuclei which pass through our universe at a speed close to that of light. The low-energy ones come from the sun or our galaxy, but the origin of the highest-energy particles has been debated since their discovery 50 years ago: are they from the Milky Way or distant extragalactic objects?
The question has just been settled by studying 30 000 cosmic particles with an energy a million times greater than that of protons accelerated at the LHC . They were detected between 2004 and 2016 with the largest cosmic ray observatory ever built, the Pierre Auger Observatory, in Argentina.
Study of the arrival directions of these particles shows that at these energies, the flux of cosmic rays coming from a sky region located 120 degrees from the galactic centre, is approximately 6 % higher than if the flux were perfectly uniform. This direction cannot be linked with potential sources in the galactic plane or at its centre.
This discovery clearly indicates an extragalactic origin for these cosmic particles, as the pattern observed in the sky is no mere coincidence, with a probability of one in five million. However, this study does not yet precisely locate the sources. Indeed, the region brightest in cosmic rays, covers a large part of the sky, where the number of galaxies is relatively high. Furthermore, the Milky Way's magnetic field deflects the trajectories of these charged particles and covers their tracks.
Research is currently being conducted on a much larger collection of ultra-high-energy cosmic rays and could provide some answers. At the same time, an upgrade programme is underway at the Pierre Auger Observatory and should make it possible to more clearly identify these sources.
The Pierre Auger Observatory
400 scientists from 18 countries are involved in the Pierre Auger Collaboration, which develops and runs the observatory with the same name. French laboratories contributing to it are:
- the Institute of Nuclear Physics at Orsay (CNRS/Université Paris-Sud);
- the Nuclear and High-Energy Physics Laboratory (CNRS/UPMC/Université Paris Diderot);
- the Laboratory of Sub-Atomic Physics and Cosmology (CNRS/Université Grenoble Alpes/ Grenoble INP).
One of the 1 600 detectors at the Pierre Auger Observatory
The flux of very high-energy cosmic rays (over 2 joules) is approximately 1 per square kilometre per year. When these rays collide with molecules in the upper atmosphere, they create a cascade of more than 10 billion secondary particles, called an air shower, which can extend over more than 40 square kilometres when it reaches the ground. The Pierre Auger Observatory detects some of these secondary particles (electrons, photons and muons) through an array of 1 600 detectors – tanks of pure water spaced 1.5 kilometres apart which cover an area of 3 000 square kilometres in the Argentine pampas (or slightly more than the size of Luxembourg). By comparing the arrival times of the particles in the different detectors, it can be determined where the cosmic ray that produced the air shower comes from.
The Pierre Auger Observatory in Argentina is the world’s largest detector of cosmic rays. It bears the name of the French physicist who first observed air showers in 1938.
Reference
Observation of a large-scale anisotropy in the arrival directions of cosmic rays above 8 × 1018 eV, The Pierre Auger Collaboration. Science, 22 September 2017. DOI: 10.1126/science.aan4338