As you can see from the previous Futura article below, it’s been a century since the noosphere discovered the existence of. This has made it possible to advance our knowledge of elementary particles and, in passing, to demonstrate the existence of antimatter before the particles and the fleeting existence demonstrated in cosmic rays, are produced by collisions of particles 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 today’sbut also because they provide information on phenomena . The study of for example, can help us understand the supplied with by in rotation accreting matter.
But there is a catch, as Futura already explained. Cosmic rays are overwhelmingly charged particles, which means that inturbulent inside the galaxies they are deflected by these fields and move there by carrying out a Brownian and therefore . Clearly, the direction from which a very energetic proton seems to come on the celestial vault, creating a shower of secondary particles by colliding with a nucleus of the high may have nothing to do with its place of origin on the same vault of heaven.
Fortunately, theare clever and they have equipped themselves with a tool and a strategy allowing them to trace the origin of some of these high energy in the . They have just published an article on this subject, an open-access version of which can be found on .
The PeVatrons at the origin of certain cosmic rays would indeed be supernovae. To obtain 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’s Goddard Space Flight Center
Protons more than 100 times more energetic than at the LHC
This tool is thegamma in the space of the baptized Fermi, in honor of the famous Italian who proposed the first of the mechanisms of cosmic ray acceleration, mechanisms which one finds associated with the shock waves of the explosions of supernovae in the interstellar medium.
A few years ago, as explained in detail in the Futura article below, Fermi’s observations of supernova remnants had already confirmed the existence of the advanced mechanisms for cosmic protons, which are elsewhere the major component of cosmic rays, even if one can findand nuclei.
Today, astrophysicists therefore explain that they have similarly put to use about 12 years of gamma flux measurements by Fermi concerning a remnant ofand that these measurements confirmed that at least this remainder was indeed a proton accelerator allowing to give them energies at least equal to the PeV, that is to say at least 100 times the energy of an accelerated proton in the LHC.
This supernova remnant, named G106.3+2.7, is therefore an authentic PeVatrons and it is in theof Cepheus, a circumpolar constellation of the at about 2,600 from . It contains in its heart a called J2229+6114 which we have every reason to think that like all the other pulsars, it is a left by the explosion of a star at the origin of the supernova remnant G106.3+2.7.
The researchers established thein gamma photon energy between 100 and 100 TeV by studying the data collected by Fermi. This spectrum is not compatible with that of gamma photons which would be mainly produced by high energies colliding with photons from the by giving them part of its energy according to an inverse Compton effect (we know that pulsars are accelerators of electrons and ). If it were electrons, it would contradict the shape of the spectrum in the domain and X 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 ofNeutral π, π mesons produced by collisions involving protons at energies up to and exceeding the PeV.
Origin of cosmic rays: Fermi confirms the track of supernovae
Article by Laurent Sacco, published on 02/18/2013
It has been assumed for decades: at least some of the cosmic rays come from proton acceleration mechanisms in supernova remnants. After years of observations in the field ofwith the Fermi telescope, astrophysicists have just confirmed the existence of accelerated protons at large in two supernova remnants, IC 443 and W44.
In 1912, the Austrian physicist Victor Franz Hess discovered the existence of cosmic rays. Using experiments carried out inhe finds that the rate of present in the atmosphere increases with altitude whereas until then we imagined the opposite, since it is the which houses the radioactive elements. These measurements at altitude therefore demonstrate that there is ionizing radiation coming from space and striking the upper layers of the atmosphere.
In the decades that followed, the study of cosmic rays made it possible to discover new elementary particles, such as pions andbefore we built after the Second World War powerful enough to produce them directly in the laboratory.
There must be particle accelerators in space
The question of the origin of these rays naturally arose and, as early as 1949, the great physicistproposed mechanisms for the acceleration of charged particles in magnetized. Subsequently, it was generally accepted that cosmic rays probably owe their existence to supernovae explosions and that Fermi mechanisms, collectively referred to as Fermi acceleration, must be at work in supernovae remnants. Basically, successive passages of charged particles through the front of the shock wave caused by the explosion of a supernova, due to Brownian movements, can sometimes lead to a clear acceleration for some of them.
Unfortunately, these hypotheses are difficult to test. Cosmic rays are made up of 90% protons, the rest being electrons and nuclei. They are subject to the effect of magnetic fields sometimesduring their movements in the Milky Way, which has the effect of making their trajectories very complex, a bit like that, again, of a particle following a Brownian movement. It is therefore difficult to associate a precise source on the celestial vault with showers of secondary particles, produced by cosmic rays hitting nuclei in the upper atmosphere.
Two supernova remnants under Fermi’s gamma eye
A recently published article onby members of the Fermi collaboration, using the bearing the name of the great Italian physicist, has nevertheless just made a significant 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 of which they observed, over a period of 4 years, two supernova remnants, and W44.
This video explains why Fermi observations help unravel the mystery of the origin of cosmic rays. To obtain a fairly accurate French translation, click on the rectangle with two horizontal bars at the bottom right. The English subtitles should then appear, if they haven’t already. By simply hovering the mouse over the rectangle, you should see the phrase “Translate subtitles”. Click to bring up the menu for choosing the language, choose “French”, then click on “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, gamma rays are emitted from these clouds, visibly bombarded by energetic particles from supernova remnants. But, problem, a priori, electrons and protons can both be responsible for thesegamma. If they are due to accelerated electrons then one should not seek in the natural proton accelerators, which constitute 90% of cosmic rays as we have said.
The pion gamma decay test
However, there is a way to decide between the hypotheses. If protons are indeed the cause of gamma emissions, part of their spectrum must be slightly different from that caused by electrons. The reason for this is that sufficiently energetic protons, upon collision with nuclei, produce neutral pions which decay into gamma photons, whereas very fast electrons emit these photons directly. The precise measurements carried out with Fermi ended up showing that the trace of the pions producing the gamma emissions was indeed there. The protons accelerated to very high speeds in the remains of supernovae are indeed responsible for the observed gamma radiation.
The thesis explaining the origin of at least a non-negligible part of cosmic rays by supernovae explosions therefore comes out very reinforced. The riddle is still not completely solved because there areat very high energies that cannot be explained by invoking supernova remnants. We tried to involve at the heart of galaxies, but this explanation remains problematic to this day.