Cosmic radiation
Cosmic radiation refers to a stream of very high-energy subatomic particles that constantly reach Earth from space. Contrary to what its name suggests, it is not electromagnetic radiation like light, but a stream of material particles— mainly protons and atomic nuclei — traveling at speeds close to the speed of light.
Where does it come from?
There are many sources of cosmic radiation, and they depend on the energy of the particles. Low-energy particles come mainly from the Sun, in the form of solar wind. Particles with intermediate energies are associated with supernovae and supernova remnants in our galaxy. The highest-energy particles—ultra-high-energy cosmic rays—appear to come from extragalactic sources such as active galactic nuclei, although their exact origin remains a subject of debate.
What Happens in the Atmosphere
When a cosmic ray particle enters Earth’s atmosphere, it collides with air molecules and produces a cascade of secondary particles— muons, electrons, and photons—that travel toward the ground. These atmospheric showers can cover several square kilometers and are detected by networks of ground-based detectors, such as thePierre Auger Observatory in Argentina.
Importance in Astrophysics
Cosmic rays are a direct messenger from the violent universe. They carry information about the acceleration processes occurring in the most energetic objects in the cosmos. It also plays a role in interstellar chemistry by ionizing gas clouds and enabling certain chemical reactions that contribute to the formation of complex molecules.
Did you know?
Cosmic radiation passes through your body constantly. At normal altitudes, you receive about 0.4 millisieverts per year from cosmic radiation—which is about 10% of the total annual natural dose. Airline pilots and astronauts receive much higher doses.
Frequently Asked Questions
Is cosmic radiation dangerous?
At ground level, the dose is low and considered safe. At high altitudes or in space, it increases significantly and poses a real risk to astronauts on long missions, particularly to Mars.
Can cosmic radiation be detected?
Yes. Specialized detectors measure the secondary particles produced in the atmosphere. Networks of detectors such as thePierre Auger Observatory cover thousands of square kilometers to detect the rarest and highest-energy events.
What is the difference between cosmic radiation and electromagnetic radiation?
Electromagnetic radiation (light, X-rays, radio waves) consists of massless photons. Cosmic radiation consists of material particles—protons, electrons, atomic nuclei—that have mass and an electric charge.