“Our observations show that Sun-like stars actually create lithium later in their lives, after they have swelled to become red giants. This means that the Sun itself will also manufacture lithium about five billion years in the future,” said Dr. Yerra Bharat Kumar from National Astronomical Observatories of the Chinese Academy of Sciences about the “lithium-rich” red giants first discovered about 40 years ago that create up to 1,000 times as much lithium as other giant stars. Yet how they create their lithium remains a mystery. The amount of lithium produced in just one of these giants would be enough to make electric car batteries for 20,000 trillion cars.
The lithium in your screen and your mobile phone’s battery was the only metal produced in the Big Bang that created the universe 13.7 billion years ago. While other elements have been produced in copious amounts by stars since then, the amount of lithium has increased relatively little. The source lithium is still a subject of scientific debate with some coming from high-energy cosmic rays hitting heavier elements like carbon and oxygen in interstellar space and breaking them up into lighter atoms.
But lithium is fragile and easily destroyed in the violent interiors of stars. Astronomers’ observations of lithium on the surface of stars has confirmed that it is gradually destroyed as stars get old where it is too hot for it to survive, so lithium content generally decreases as the stars age.
However, a new study led by professor Zhao Gang and Kumar provides a fresh understanding of both how lithium is made, and how it is destroyed.
“Quite a Special Element”
“Lithium is quite a special element,” said Kumar, first author of research that studied the lithium content of hundreds of thousands of Sun-like stars to understand how this element changes over time in stars. “Our study challenges the idea that stars like the Sun only destroy lithium through their lives.”
Since lithium is such a sensitive element, it is very useful for understanding stars. It acts as a tracer for what is happening inside stars. To better understand this extremely fragile element, researchers used data from a huge Chinese stellar spectroscopic survey based on The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). The survey is currently building a database of the spectra of ten million stars.
This study also utilized data from Australian star survey known as GALAH. “By looking at starlight, we can determine what the stars are made of,” said Kumar. “Models show that our current theories about how stars evolve do not predict this lithium production at all. Thus, the study has created a tension between observations and theory.”
“Our findings will help us to better understand and model Sun-like stars,” said professor. Zhao Gang, the co-corresponding author. “Since the newly created lithium will end up being blown off the star in stellar winds, it will also help us understand how these stars contribute to the lithium content of our Galaxy, and to planets like Earth,” said Zhao.
More information: Yerra Bharat Kumar et al, Discovery of ubiquitous lithium production in low-mass stars, Nature Astronomy (2020). DOI: 10.1038/s41550-020-1139-7
Image credit: Shutterstock Red Giant Star