Exploding star solves cosmic mystery
Y. Beletsky (LCO)/ESO

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Exploding star solves cosmic mystery

Astronomers have seen for the first time an exploding star—a nova—that seems to churn out lithium, solving a nagging cosmic mystery. The very oldest stars in the universe seem to have much less lithium than they should, and young stars have too much. A number of different solutions have been put forward to explain the deficit in old stars, such as that the production of lithium in the first 15 minutes after the big bang was different than we think, or that old stars are hoarding lithium in their cores so that they appear to have less on their surfaces where it can be measured. The overabundance in young stars poses a different puzzle, because fusion reactions in the cores of stars tend to consume lithium, not create it. Astronomers suggested back in the 1970s that lithium could be produced in novae, stellar explosions that don’t result in the destruction of their star like supernovae do. A nova occurs when a burnt out star known as a white dwarf has a binary companion star and the dwarf’s greater gravity steals hydrogen from its neighbor. The hydrogen builds up in a layer on the white dwarf’s surface until there is enough to spark hydrogen fusion, blowing the surface layer out into space and briefly making the star very bright. The conditions in that fusion reaction could produce lithium, and today astronomers observing Nova Centauri 2013 (pictured)—the brightest nova this century and easily visible to the naked eye—report seeing a clear signature of lithium being flung out from the star at 2 million kilometers per hour. Although the amount of lithium was tiny, if all novae throughout the history of the universe produced similar amounts that would provide enough to explain the amount we see in our galaxy today, the team states in Astrophysical Journal Letters.