High Energy Astrophysics and the Origin of Cosmic Rays
The origin of Galactic cosmic-ray ions has remained an enigma for almost a century. Although it has generally been thought that they are accelerated in the shock waves associated with powerful supernova explosions—for which there have been recent claims of evidence—the mystery is far from resolved. Cosmic rays, which are mostly protons, but also other ions and electrons, permeate our Galaxy and rain down on earth continuously, night and day. Although cosmic rays were discovered almost a century ago, back in the balloon age, their origins remain unclear even now. Almost no effort has been spared in pursuing this long-standing mystery: satellites, rockets and balloons have been launched, and enormous detector arrays have been installed on the ground and even under mountains and seas. I will give a historical overview of the search for the mysterious origin of cosmic rays and a report on the current status.