Puzzle about stars solvedDate: 11 July 2020 Tags: Space
A forty-year-old puzzle regarding the production of lithium in stars has been solved by Indian researchers.
Planets were known to have more lithium than their stars — as is the case with the Earth-Sun pair. However, leading to a contradiction, some stars were found that were lithium-rich.
The new work shows that, in fact, when stars grow beyond their Red Giant stage into what is known as the Red Clump stage, they produce lithium in what is known as a Helium Flash and this is what enriches them with lithium.
Lithium was first produced in the Big Bang, around 13.7 billion years ago when the universe came into being, along with other elements.
While the abundance of other elements grew millions of times, the present abundance of lithium in the universe is only four times the original [Big Bang] value. It is actually destroyed in the stars.
About 40 years ago, a few large stars were spotted that were lithium-rich. This was followed by further discoveries of lithium-rich stars, and that posed a puzzle — if stars do not produce lithium, how do some stars develop to become lithium-rich?
The planet engulfment theory was quite popular. For example, Earth-like planets may increase the star’s lithium content when they plunge into the star’s atmosphere when the latter become Red Giants.
Until now, it was believed that only about 1% of giants are lithium-rich. Secondly, the team has shown that as the star evolves beyond the Red Giant stage, and before it reaches the Red Clump stage, there is a helium flash which produces an abundance of lithium.
Lastly, they set a lower limit for helium abundance which will classify the star as “lithium-rich”. This value is about 250 times lower than the previous limit.