Scientists at the Indian Institute of Astrophysics (IIA) have uncovered hints to the riddle of high Lithium content in evolved stars. On Earth, the element can be found in trace levels.
Scientists have long been puzzled by the presence of lithium in evolved stars, as models suggested that the element would have been annihilated in the star’s heated plasma. However, Deepak from the Indian Institute of Astrophysics (IIA) in Bangalore and Professor Emeritus David L. Lambert from the University of Texas at Austin have established that lithium generation is linked to helium burning in these stars’ cores.
According to the researchers, all lithium-rich stars burn helium in their cores, according to a study published in the Monthly Notices of the Royal Astronomical Society.
“About four decades ago, a red giant with extraordinarily high lithium abundance at its surface was discovered. In all other respects, this red giant was of normal composition. Early follow-up investigation of lithium among red giants showed that just about one per cent of sun-like red giants had a lithium-enriched surface. The questions on processes that led to a 100-fold or so increase in the lithium abundance in this exceptional red giant and reason behind this selective enrichment of lithium in the one per cent of red giants intrigued us,” Deepak explains.
The two researchers used data from the Australian Astrophysical Observatory’s comprehensive assessment of the makeup of red giants. The scan yielded a database of around 5,00,000 stars with well-defined physical and chemical attributes, including lithium abundances.
They next divided the stars into groups based on their mass and metallicity, and looked for lithium-rich giants within these groupings. In a release, the Ministry of Science and Technology said, “This exercise, done for the first time on such a big scale and across such a wide range of mass and metallicity, exposes the uncommon existence of lithium-rich giants in all the Sun-like low-mass stars.”
The comparison revealed that all lithium-rich stars have helium burning at their cores.
Meanwhile, researchers coupled knowledge about oscillations in star interiors with lithium abundance to determine the genesis of these lithium-rich stars. They based their findings on the notion of a series of nuclear events involving a collision between two stable helium isotopes, which resulted in the formation of a stable lithium isotope.
They gathered asteroseismic data (information about oscillations in the interiors of stars) for big stars with lithium abundances that had been measured.