The enigma of cosmic rays-2

Part 1¹ of the article discussed the discovery and observed properties of cosmic ray particles. These energetic particles are produced during violent astronomical events. We discuss possible sources of cosmic rays detected on Earth in this article. Supernovae explosions of dying stars are believed to produce cosmic rays with low energy. The detection of ultra-high energy cosmic rays is however difficult to explain. On one hand, they must originate outside our Galaxy and on the other, the cosmic microwave background radiation pervading the universe makes it difficult for them to travel large distances in intergalactic space. So, they must be produced in the neighbourhood of our Galaxy, but are there enough energetic phenomena taking place in this region of the universe? Biman Nath is an astrophysicist at the Raman Research Institute, Bangalore.