Bengaluru scientists find out where the Lithium in your smartphone came from

How did lithium – a metal integral to modern life, thanks to long-duration batteries – come to the Earth?

This has been a long-held scientific puzzle that has now been cracked by astrophysicists from Bengaluru in collaboration with their international partners.

Analysing data from a galactic survey of 100,000 stars, researchers at the Indian Institute of Astrophysics have discovered that all low-mass Sun-like stars produce lithium from an internal process known as helium flash when the gas was cooked at high temperature inside the stellar ovens.

Such lithium generating stars would have a mass of up to two Solar masses or twice the weight of the Sun.

The discovery published in the Nature Astronomy on Monday sets aside a four-decades-old theory according to which only 1% of the stars produce lithium though little was known about the process.

“Our discovery shows that any low mass stars where helium flash takes place will produce lithium. This challenges the long held idea that stars only destroy lithium during their lifetime. Our work also implies that the Sun itself will manufacture lithium in the future, which is not predicted by any models, indicating that there is some physical process missing in stellar theory.” B Eswar Reddy, IIA professor and one of the authors of the paper told DH.

The origin of lithium - the only metal created from the Big Bang 13.7 billion years ago – was a mystery because stars with a temperature of 2.5 million degrees Kelvin annihilate it, leaving the scientists to wonder where it comes from.

Over the course of time, the lithium content in the physical Universe has increased by about a factor of four which is meagre compared to the rest of the elements like carbon, nitrogen, oxygen, iron, nickel and so on which grew about a million times over the lifetime of the Universe.

Stars are primary contributors to this significant enhancement of these heavier elements through mass ejections and stellar explosions. Lithium, however, is understood to be an exemption! As per the current understanding, based on today’s best models, lithium in stars like the Sun only gets destroyed over their lifetime.

"This was a great puzzle that existed for four decades because as soon as lithium was produced, it was destroyed,” Reddy said.

Partnering with the researchers from the Chinese Academy of Sciences, Monash University, Australia and Institute for Advanced Studies, Princeton, the Bengaluru astrophysicists have not only demonstrated the genesis of lithium in the cosmic cauldrons, but also proposed an explanation for the underlying process.

"The result is potentially very important for the cosmos since the observations question the existing wisdom that limits the amount of lithium that could be expected to be formed and retained in stars (stellar nucleosysnthesis). It points to possible lack of understanding how light nuclei like lithium are cooked in the stellar furnaces," commented astrophysicist Tarun Sourdeep, a professor at the Indian Institute of Science, Education and Research, Pune, who is not associated with the study.

Reddy said the work is far from over as the team would now seek to find an answer to another mystery – how did the lithium survive in such stars with superlative temperature.