Cosmic rays is a collective term for high energy particles such as x-ray photons, high energy gamma radiation electrons and energetic protons which originate mainly outside the solar system. Most details about cosmic radiation are still being studied by scientists but most likely due to the large amount of energy cosmic rays carry they most likely originate from supernovas or the collisions of massive stars.
When cosmic rays strike the Earth's atmosphere secondary particles such as muons are created. These secondary particles have been used as evidence for Einstein's relativistic time dilation. Such secondary particles have a half-life where they should decay before reaching the Earth's surface. However, since the secondary particles are moving close to the speed of light their time frame reference is slower than Earth observers.