He notes that should produce radiation capable of ionizing the helium contained in the interstellar medium.

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He chose this because the supernova that created it blew a giant bubble, known as the Vela nebula, out of the surrounding interstellar medium, and that bubble is big enough to stand in for the infinite sheet of gas.

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"The interesting thing is that the protons don't get accelerated in the supernova explosion itself, but they get accelerated in what we call the remnant - the shockwave that is created in the explosion and then moves away through the interstellar medium, " said Dr Funk.

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