With the help of special telescopes, researchers have observed a cosmic particle accelerator as never before. Observations made with the gamma ray observatory H.E.S.S. in Namibia show for the first time the course of an acceleration process in a stellar process called a nova, which comprises powerful eruptions on the surface of a white dwarf. A nova creates a shock wave that tears through the surrounding medium, pulling particles with it and accelerating them to extreme energies. Surprisingly, the nova "RS Ophiuchi" seems to cause particles to accelerate at speeds reaching the theoretical limit, corresponding to ideal conditions. The research has been published in the journal Science.