Where do ultrahigh-energy particles come from?

Active Galactic Nuclei are the most likely candidates for the source of the highest-energy cosmic rays observed on the Earth. The origin of these ultra high energy (UHE) cosmic rays has been a long standing mystery in Astrophysics. Active Galactic Nuclei (AGN) consist of black holes with a huge mass, between a billion to ten trillion times that of our Sun, which keeps growing by gravitationally attracting gaseous matter. During the in-fall of matter into the black hole, electromagnetic radiation is emitted, such as radio, infrared, optical, ultraviolet, X-rays, or gamma rays, in large amounts. AGNs are the most luminous objects in the Universe. They also have been investigated as sources of very high-energy cosmic rays, though the exact mechanism of how they could accelerate particles to energies 100 million times higher than the most powerful particle accelerator on Earth is still not well understood. read less