The Pierre Auger Collaboration studied the directions of arrival of more than 30 thousand of cosmic ray particles and revealed anisotropy with significance of 5.2 standard deviations, which corresponds to one in 2 million possibility to be just a coincidence, with a maximum in a direction where a large number of distant galaxies is located. While this discovery (recently published in Science) clearly confirms the extra-galactic origin of the particles, we cannot infer particular sources – it just points to a general area in the sky where the particles come from, because even at energies as high as those of detected particles magnetic fields in the universe can deflect the particles on their way by up to several tens of degrees. However, no realistic configuration of the magnetic field can be imagined that would allow their original direction from the center of our galaxy or in its plane. Even more energetic particles have been observed than those used in the present study (some bear energies comparable to a well-hit tennis ball). The deflections of flight of such particles will be even smaller and their detection would point better to their location of origin. Nevertheless, such particles are more rare and research aiming at revealing their sources is in progress. The ability to determine the nature of the particle is crucial in this search and his ability will be considerably improved during on-going upgrade of the Pierre Auger Observatory.
The discovery has been recognized by the award “Physics World Top Ten Breakthroughs of 2017” by editors of Physics World.