A comparison between observations of the Gum Nebula and Chevalier's (1974) model for an evolving supernova remnant suggests that the Gum Nebula may be a 1-million-year-old expanding gas shell which was produced by an explosion with energy of 5 by 10 to the 51st power ergs in a medium of density 0.25 per cu cm and which is now being heated and ionized by the ultraviolet flux from Zeta Pup and Gamma-2 Vel. The stellar wind from Zeta Pup may also be an important energy source within the nebula.
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R. J. Reynolds (1976) studied this question.