The latest contender for the mysterious cosmic rays which are detected regularly but have no obvious source is perhaps gas left over from the Big Bang. By using the Very Large Array of radio telescopes in New Mexico, a team of astronomers led by Joydeep Bagchi of the University of Pune in India observed giant shock waves. These waves could have been formed by the collision of two gigantic galactic clusters about a billion years ago, but they also may have been created through the interaction of "filaments" of left-over gas from the Big Bang running into the much hotter gas given off by the cluster. Such a cold/hot boundary would be excellent at accelerating particles to stupendous speeds, and are therefore prime candidates for the mysterious cosmic rays.

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