Exploding white dwarfs produce most of the lithium in the universe

GRANADA, Spain, Nov. 3 (UPI) -- Lithium, like almost every element, is produced by astronomical phenomena. Until now, scientists weren't sure which phenomena produced lithium, the lightest solid element in the universe.

The answer is novae -- periodic stellar explosions in binary star systems with a white dwarf.

Recently, a team of researchers at the Institute of Astrophysics of Andalusia detected a significant amount of beryllium-7 at the center of an exploding white dwarf, nova Sagittarii 2015 N.2.

Beryllium-7 is an unstable element that, after 53.2 days, decays into lithium.

Lithium is one of only a few elements forged almost immediately after the Big Bang. The explosion that birthed the universe also produce large amounts of hydrogen and helium, and trace amounts of lithium and beryllium.

The newer, heavier elements were produced by stellar fusion. Over time, the stellar life cycle yielded more and more elements. Supernovae -- explosive stellar deaths -- spewed elements that became new elements inside new stars.

"But lithium posed a problem: We knew that 25 percent of existing lithium comes from primordial nucleosynthesis, but we were not able to trace the origins of the remaining 75 percent," researcher Luca Izzo explained in a news release.

Thanks to the observational prowess of the Very Large Telescope and its UVES instrument, astronomers located the origin of the missing 75 percent. Researchers watched the explosion of Sagittarii 2015 N.2 for 24 days, tracking the growing beryllium-7 signal.

Beryllium-7 had been seen in novae before, but never in such a large amount.

"We're talking about an amount of lithium 10 times greater than that in the sun," said Izzo. "With these amounts in mind, two similar novae a year would suffice to account for all the lithium in the Milky Way. Novae seem to be the predominant source of lithium in the universe."

Researchers detailed their discovery in a new paper published in the Monthly Notices of the Royal Astronomical Society Letters.