Astronomers find clue to mystery behind high abundance of Lithium in some evolved stars

Scientists have found a clue to the mystery behind the high abundance of Lithium - a key element used in rechargeable batteries -  in some evolved stars, the Ministry of Science and Technology informed in a press release on November 30.

According to the release, this is the first time, that astronomers have found clues about the mystery as to why there is a high abundance of lithium in evolved stars.

"For more than four decades, astronomers have known that a class of stars have an anomalous amount of Lithium on their surface. The reason and processes behind the high abundance of Lithium in about 1% red giants has remained a puzzle since the models of how stars evolve predict the Lithium must have been destroyed in the hot plasma of the star," the release stated, adding that a group of scientists have found a clue to solve the mystery. 

"Mr Deepak from the Indian Institute of Astrophysics (IIA) Bangalore, an autonomous institute of the Department of Science & Technology (DST), Government of India and Professor Emeritus David L Lambert from the University of Texas at Austin and an Honorary Fellow of IIA Bangalore have for the first time confirmed that all the lithium-rich stars are burning helium in their core. They speculated in their paper published in the journal MNRAS that lithium production is linked to the violent helium-core flash," the release informed. 

Scientists confirm lithium in red giant stars

"About four decades ago, a red giant with extraordinarily high lithium abundance at its surface was discovered. In all other respects, this red giant was of normal composition. Early follow-up investigation of lithium among red giants showed that just about 1% of sun-like red giants had a lithium-enriched surface", Deepak said, as per the press communique.

"The questions on processes that led to a 100-fold or so increase in the lithium abundance in this exceptional red giant and reason behind this selective enrichment of lithium in the 1% of red giants intrigued us", he added. 

The abundance of lithium was confirmed after the experts conducted a large survey named GALAH, which provided a collection of about 500,000 stars with well-determined physical and chemical properties, including lithium abundances. The stars targeted in this survey were then separated into different mass and metallicity ranges and then searched for lithium-rich giants in order to find if the enrichment of lithium in red giants favours any particular mass and metallicity.

"This exercise, done for the first time on such a large scale and across a wide range of mass and metallicity, reveals the rare presence of lithium-rich giants in all the Sun-like low-mass stars", the Ministry said. 

Moreover, to determine the origin of lithium-rich giant stars, the experts conducted another study, that involved information about oscillations in stars' interiors with their lithium abundances. In order to find the origin, experts gathered the interior oscillations data in red giant stars that were found to have an abundance of lithium. Analysis of the said data made the scientists confirm that the stars definitely had no shortage of lithium and that these stars have helium burning in their core.

Image: National Astronomical Observatory of Japan