Origin of cosmic rays: supernovae would be PeVatrons!

La vue de Fermi sur le ciel gamma s'améliore constamment. Cette image du ciel entier comprend trois années d'observations par le télescope à grande surface de Fermi (LAT). Il montre comment le ciel apparaît à des énergies supérieures à 1 milliard d'électronvolts (1 GeV). Des couleurs plus claires indiquent des sources de rayons gamma plus lumineuses. Une lueur diffuse remplit le ciel et est la plus brillante le long du plan de notre Galaxie (au milieu). Les sources discrètes de rayons gamma comprennent des pulsars et des restes de supernovae dans notre Galaxie ainsi que des galaxies lointaines alimentées par des trous noirs supermassifs. © Collaboration Nasa/DOE/Fermi LAT

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[EN VIDÉO] A “black widow” pulsar devours its mate When it comes to spiders, black widow spiders are the ones that devour their mates after mating. And astronomers have observed similar behavior in the sky. When a pulsar and a low-mass star form a binary system. Faced with the radiation emitted by the pulsar, the star has little chance of surviving for long. (in English) © Nasa Goddard As you can see in the previous Futura article below, it’s been a century since the noosphere discovered the existence of cosmic rays. This has made it possible to advance our knowledge of elementary particles and, incidentally, to demonstrate the existence of antimatter before exotic particles, and the fleeting existence demonstrated in cosmic rays, were produced by particle collisions at higher and higher energies. the study of cosmic rays continues, already because some of the particles present have been accelerated to energies impossible to reach even with the LHC today, but also because they allow us to provide information about astrophysical phenomena. The study of cosmic neutrinos, for example, can help us understand the active cores of galaxies, energized by the rotation of supermassive black holes that accumulate matter, but there is a catch, as Futura already explained. Cosmic rays are overwhelmingly charged particles, which means that in turbulent magnetic fields within galaxies they are deflected by these fields and move through them in Brownian and therefore stochastic motion. Clearly, the direction from which a highly energetic proton in the sky appears to be coming, creating a shower of secondary particles upon colliding with a nucleus in the upper atmosphere, may have nothing to do with its place of origin in the same celestial vault. Fortunately, astrophysicists are smart and have acquired a tool and a strategy that allows them to trace the origin of some of these high-energy protons in the Milky Way. They have just published a paper on this topic, an open access version of which can be found on arXiv. The PeVatrons at the origin of certain cosmic rays would in fact be supernovae. For a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © NASA Goddard Space Flight CenterProtons more than 100 times more energetic than at the LHCA tool is NASA’s gamma-ray telescope in space, named Fermi, after the famous Italian physicist who proposed the first of the mechanisms of ‘acceleration of cosmic rays, mechanisms found associated with The shock waves of supernova explosions in the interstellar medium of Fermi on supernova remnants had already made it possible to consolidate the existence of the advanced mechanisms of cosmic protons, which are also the main component of cosmic rays, although positrons and nuclei can be found. So today astrophysicists explain that they similarly took advantage of some 12 years of Fermi gamma flux measurements of a supernova remnant and that these measurements confirmed that at least this remnant was in fact a proton accelerator that gives them energies at least equal to the PeV, i.e. at least 100 times the energy of a proton accelerated at the LHC. This supernova remnant, called G106.3 +2.7, is therefore a true PeVatrons and is in the constellation ·lation of Cepheus, a circumpolar constellation of the northern hemisphere, about 2,600 light years from the Solar System. It contains at its heart a pulsar called J2229+6114 which we have every reason to think is, like all other pulsars, a neutron star left by the explosion of a star at the origin of the supernova remnant G106 .3+2.7 . The researchers established the energy spectrum of gamma photons between 100 GeV and 100 TeV by studying data collected by Fermi. This spectrum is not compatible with that of gamma photons which would be produced mainly by high-energy electrons colliding with photons of fossil radiation giving them part of their energy according to an inverse Compton effect (we know that pulsars are electron accelerators and positrons). . If they were electrons, this would contradict the shape of the spectrum in the radio and X domain associated with G106.3 + 2.7. As a few years ago, we therefore come to the conclusion that the gamma photons observed by Fermi come from the decay of neutral π mesons, π mesons produced by collisions involving protons at energies that can reach and exceed the PeV.Origin of cosmic rays: Fermi confirms supernova trailArticle by Laurent Sacco, published on 18/02/2013 It has been assumed for decades that at least some cosmic rays come from proton acceleration mechanisms in supernova remnants. After years of observations in the gamma-ray field with the Fermi telescope, astrophysicists have just confirmed the existence of protons accelerated to high speeds in two supernova remnants, IC 443 and W44. In 1912, Austrian physicist Victor Franz Hess discovered the existence of cosmic rays. From experiments carried out in balloons, he observed that the level of ions present in the atmosphere increased with altitude, while until then he had imagined the opposite, since it was the earth’s crust that housed the radioactive elements. These measurements at altitude show, therefore, that there is ionizing radiation coming from space and affecting the upper layers of the atmosphere. In the following decades, the study of cosmic rays made it possible to discover new elementary particles, such as pions and muons, before we built after World War II accelerators powerful enough to produce them directly in the laboratory There must be particle accelerators in space The question of the origin of these rays arises, of course, and, already in 1949, the great physicist Enrico Fermi proposed mechanisms to accelerate charged particles in magnetized interstellar clouds. Subsequently, it was generally accepted that cosmic rays probably owe their existence to supernova explosions and that Fermi mechanisms, collectively known as Fermi acceleration, must be at work in supernova remnants. Basically, the successive steps of charged particles across the shock wave front caused by a supernova explosion, due to Brownian motions, can sometimes lead to a strong acceleration for some of them. Unfortunately, these hypotheses are difficult to test. Cosmic rays are made up of 90% protons, the rest are electrons and nuclei. They are subject to the effect of sometimes turbulent magnetic fields during their movements in the Milky Way, which has the effect of making their trajectories very complex, somewhat like, again, a particle following a brownian motion Therefore, it is difficult to associate a precise source in the sky with showers of secondary particles, produced by cosmic rays impacting the cores of the upper atmosphere. Two supernova remnants under Fermi’s gamma eye A recent article published in the archive by members of the Fermi collaboration, using the gamma telescope named after the great Italian physicist, has just made an important contribution to the elucidation of the enigma of the origin of cosmic rays. To do this, the researchers took advantage of the fact that gamma rays are not deflected by galactic magnetic fields. As a result, they observed, over a period of 4 years, two supernova remnants, IC 443 and W44. This video explains why Fermi’s observations help unravel the mystery of the origin of cosmic rays. For a fairly accurate French translation, click on the rectangle with two horizontal bars in the lower right. Then the English subtitles should appear, if they haven’t already. Simply hover your mouse over the rectangle, you should see the phrase “Translate Subtitles”. Click to open the menu to choose the language, choose “French” and then click “OK”. © Nasa Explorer The shock waves associated with the explosions of the two supernovae that produced these remnants propagate in cold molecular clouds. As a result, these clouds emit gamma rays, visibly bombarded by energetic particles from supernova remnants. But, problem, a priori, electrons and protons can both be responsible for these gamma emissions. If they are due to accelerated electrons, the natural accelerators of protons, which make up 90% of cosmic rays as it was said, should not be sought in the supernova remnants. between hypotheses. If protons are really the cause of gamma emissions, a part of their spectrum must be slightly different from that caused by electrons. The reason for this is that sufficiently energetic protons, when colliding with nuclei, produce neutral pions that decay into gamma photons, while very fast electrons emit these photons directly. Precise measurements made with Fermi ended up showing that the trail of pions producing the gamma emissions was indeed there. Protons accelerated to very high speeds in supernova remnants are indeed responsible for the observed gamma radiation, the thesis that explains the origin of at least a non-negligible part of cosmic rays by supernova explosions is greatly strengthened. The puzzle is still not completely solved because there are very high-energy cosmic rays that cannot be explained by invoking supernova remnants. Attempts have been made to implicate supermassive black holes at the heart of galaxies, but this explanation remains problematic to this day. Interested in what you just read?
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