Extra Galactic Cosmic Rays
Extra Galactic Cosmic Rays are Cosmic Rays (CR) that are almost certainly too powerful to be created from sources inside our galaxy. Therefore, they are thought to come from vast distances. They are probably produced in quasars or active galactic nucleus.
They have huge energies of quadrillion to quintillions of electron volts. This is a massive energy to be carried by a single particle.
Discussion
The upper limit for these particles is an energy of 50 exa electron volts (50 EeV), because particles going faster than this lose energy to the cosmic microwave background radiation. This is called the Greisen-Zatsepin-Kuzmin limit (GZK cutoff), thru quantum mechanical effects. (See this wiki article for more details.[1]) Note that the GZK cutoff only applies to particles which travel vast distances, ~160 million light years. There are no quasars within this distance and few active galactic nucleus this close.
However, we have detected cosmic rays with higher than this energy which have not come from any direction close to an active galaxy. Thus we have found Extreme Energy Cosmic Rays for which we have no explanation as to their origins.
These cosmic rays are so powerful that no conceivable radiation protection will help, save making bases kilometres below the surface of Mars. Since we are bombarded with these particles (their secondary radiation from colliding with air atoms high in our atmosphere) on the surface of Earth they will be ignored by Martian colonists exactly as we ignore them here on Earth.
