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Lithium comes from stellar explosions

Nova blast A large amount of lithium, one of the key elements in the chemical evolution of the cosmos, is produced by stellar explosions called novae.

The findings, reported in the journal Nature, provide the first direct evidence that lithium, which is used for lithium-ion batteries in computers, smart phones and eco-cars, is produced by stellar objects.

"Understanding the way lithium is produced, means we can now understand every process of elemental production in the universe," says the study's lead author Dr Akito Tajitsu of the National Astronomical Observatory of Japan.

A nova is an extremely bright thermonuclear explosion on the surface of a white dwarf, the slowly cooling core of a star like our Sun after its run out of hydrogen and helium fuel.

Because white dwarfs have long lives and can experience multiple nova events, it means the total production of lithium will be quite large over the history of the universe, says Tajitsu.

The origin of lithium and its production process have long been uncertain.

Together with hydrogen and helium, a small amount of lithium was generated directly through Big Bang nucleosynthesis and is now produced through collisions between cosmic ray particles and gas in the interstellar medium.

Chemical evolution models and observed lithium abundances in the Milky Way indicate at least half of all the lithium is produced in old bloated stars called red giants, in their successors known as asymptotic giant branch stars, and by novae.

But lithium is very fragile at the high temperatures found in stars, and so until now there's been little direct evidence to support the idea of novae being a major source of lithium.

Lucky star

On 16 August 2013, astronomers detected the first naked-eye nova since 2007.

Located in the northern constellation Delphinus, the nova was named V339 Delphini.

Tajitsu and colleagues used the Subaru Telescope in Hawaii to study chemical signatures produced by the light coming from the nova.

They detected strong signatures for radioactive beryllium-7 being blasted out during the nova explosion.

Beryllium-7 is an unstable isotope with a half life of 53 days.

As the beryllium-7 is blasted into cooler environments away from the white dwarf, it decays into the stable isotope lithium-7.

Riddle solved

Until now, it's been difficult to understand how Lithium-7 could form and survive in extreme temperatures such as novae, says Dr Lilia Ferrario of the Australian National University who was not involved in the research.

The lithium survives because it forms away from the extreme heat of the nova explosion.

"This discovery helps solve that problem," says Ferrario

"It suggests that may be up to half of the lithium is produced during stellar evolution, which is a significant amount."

According to Ferrario, it's an important step in understanding the chemical evolution of the universe.

"This is very exciting, anything that can add to our knowledge of the origins of elements, what the universe is made of, and where we come from, is important," says Ferrario.