Astroparticles and cosmic messengers

The universe is continuously traversed by elementary and subatomic particles, which travel through space at very high speeds. Many of these reach Earth, bringing very precious information about astrophysical phenomena that produced them. When you talk about “astroparticles”, you typically refer to cosmic rays. These are high-energy particles that reach the Earth from every direction, mainly composed of protons (approximately 90%), in addition to helium nuclei (9%), and a very small percentage of atomic nuclei, electrons and, in a minimal part, antiparticles. In reality, only a small part of cosmic rays actually reaches us, thanks to the “shield” provided by the atoms of the atmosphere, which absorbs a large part of cosmic radiation (this is lucky, since prolongede xposure to the very high energies of these particles would have lethal effects on the tissues of our organism).

Artistic representation of cosmic rays (© INFN)

Detector of the Auger experiment in Argentina (© Pierre Auger Observatory)

Cosmic rays can have both a galactic and an extragalactic origin. However, precisely determining their astrophysical sources is not an easy task, since interstellar magnetic fields may easily disturb the trajectories of these particles in their path towards terrestrial telescopes. It is thought, in any case, that the most energetic are produced by some of the most extreme events of the universe, like supernovae explosionsor emissions of active galactic nuclei. Experiments that hunt down cosmic rays use various detection techniques, often indirect ones, and may be both terrestrial and space-based. For approximately 20 years, INFN has participated in the Auger experiment in Argentina, the most extensive observatory for studying cosmic rays ever built, with detectors distributed across an area of about 3,000 km2.

Cosmic neutrinos also figure among astroparticles. These are very difficult to detect due to their poor capacity for interaction with matter, but, at the same time, are carriers of direct information on some of the most extreme energy sources of the universe (often not accessible with electromagnetic telescopes).
The IceCube experiment, at the South Pole, has been active for a long time in researching very high energy astrophysical neutrinos, while the future underwater telescope for cosmic neutrinos, KM3NeT, is being built in the Mediterranean Sea. INFN is making a decisive contribution to this, in particular with the National Laboratories of the South.

The IceCube laboratory (© IceCube/NSF, Erik Beiser)

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