A forty-year-old puzzle regarding the production of lithium in stars has been solved by Indian researchers.

Try this question from CSP 2013:

Q.Consider the following phenomena:

1. Size of the sun at dusk
2. Colour of the sun at dawn
3. Moon being visible at dawn
4. Twinkle of stars in the sky
5. Polestar being visible in the sky

Which of the above are optical illusions?

(a) 1, 2 and 3

(b) 3, 4 and 5

(c) 1, 2 and 4

(d) 2, 3 and 5

Lithium nucleosynthesis in Stars

• Stars, as per known mechanisms of evolution, actually destroy lithium as they evolve into red giants.
• 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 by an Indian researcher shows that when stars grow beyond their Red Giant stage into what is known as the Red Clump stage, they produce lithium.
• This is known as a Helium Flash and this is what enriches them with lithium.

Studying lithium-rich 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 [their] star’s atmosphere when the latter become Red Giants.

Findings of the Indian research

• Indian researchers have been working on this puzzle for nearly 20 years to devise a method of measuring lithium content using low-resolution spectra in a large number of stars.
• The study demonstrated that lithium abundance enhancement among low mass giant stars is common.
• 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.

Back2Basics: Lithium

• Lithium is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the lightest metal and the lightest solid element.
• S light element commonly used today in communication device technology, it has an interesting story.
• It 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.
• The Sun, for instance, has about a factor of 100 lower amount of lithium than the Earth.

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