Production of lithium in stars
A forty-year-old puzzle regarding the production of lithium in stars has been solved by Indian researchers. Stars, as per known mechanisms of evolution, actually destroy lithium as they evolve into red giants.
What is Lithium?
• Lithium is the lightest known metal with atomic number 3. It is an element of many uses.
• According to NASA, Lithium, as well as the first and second lightest chemical elements (hydrogen and helium, respectively), are the only elements created at the birth of the universe.
• However, according to the Big Bang Theory, the universe should hold three times as much lithium as can be accounted for in the oldest stars, an issue called the missing lithium problem.
• It's used in the manufacture of aircraft. It's also used in mental health: Lithium carbonate is a common treatment of bipolar disorder, helping to stabilize wild mood swings caused by the illness.
• Lithium-ion batteries are the key to lightweight, rechargeable power for laptops, phones and other digital devices.
• Lithium is a special metal in many ways. It's light and soft — so soft that it can be cut with a kitchen knife and so low in density that it floats on water. It's also solid at a wide range of temperatures, with one of the lowest melting points of all metals and a high boiling point.
Astronomers regard lithium as fragile, easily destroyed in the hot interiors of stars. This is confirmed by observations of lithium on the surface of stars, where we see that it becomes less abundant as they age, confirming that they gradually destroy it as they evolve.
However, the 'lithium-rich giants', first discovered about 40 years ago, have lithium contents up to 1000 times higher than other giant stars. They have been a source of mystery and detailed astronomical study - eluding explanation for many decades.
According to a new study, 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 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.
Before this finding, 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. Until now, it was believed that only about 1% of giants are lithium rich.
This is the first study to demonstrate that lithium abundance enhancement among low mass giant stars is common.
The research 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.