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:
- Size of the sun at dusk
- Colour of the sun at dawn
- Moon being visible at dawn
- Twinkle of stars in the sky
- 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.
