Cosmic radiation

The flux of very energetic particles which reach us from space and fill the interstellar environment. Discovered at the beginning of the 20th century, this cosmic radiation remained a mystery for a long time. Today we think it is made up principally of protons and its origin is varied. Some particles come from the Sun, others from our galaxy, others still are of inter-galactic origin: they are violently ejected from the active cores of galaxies neighbouring the Milky Way.