Primary Cosmic Rays
Primary Cosmic Rays are charged particles that have been accelerated to enormous energies by astrophysical sources somewhere in our universe. They must be stable in order to survive the long trips through interstellar (or intergalactic) space. If they are charged, and therefore swerved by magnetic fields, it is extremely difficult to locate their source. Experiments on satellites can perform direct studies on their composition, and look for the presence of antimatter.