Some evolved stars contain Lithium, a trace element on Earth and a critical component of rechargeable batteries. For more than 40 years, the reason and mechanism for this phenomenon in about 1% of red giants (stars similar to the Sun) have remained a mystery. Lithium production, scientists hypothesize, is connected to the violent helium-core flash. According to a study conducted by researchers at the Danish Meteorological Society, lithium-rich giant stars are burning helium in their cores (DST). The DST has requested quantitative estimates of lithium production during the ignition of helium burning in red giants from theoretical astrophysicists.
Key Highlight:
- Scientists at Bengaluru’s Indian Institute of Astrophysics (IIA) and the University of Texas have discovered the mystery surrounding the high abundance of Lithium in some evolved stars.
- Lithium is a trace element on Earth and a critical component of rechargeable batteries.
- For more than 40 years, the reason and mechanism for this phenomenon in about 1% of red giants (stars similar to the Sun) have remained a mystery.
- Scientists hypothesize that lithium production is related to the violent helium-core flash.
- The study reveals the infrequent presence of lithium-rich giants in all Sun-like low-mass stars.
- The authors invite theoretical astrophysicists to provide quantitative estimates of lithium production during helium burning in red giants.
Scientists at Bengaluru’s Indian Institute of Astrophysics (IIA) and the University of Texas have discovered the mystery surrounding the high abundance of Lithium in some evolved stars. Lithium is a trace element on Earth and a critical component of rechargeable batteries.
While astronomers have known for more than 40 years that a class of stars has an abnormally high concentration of Lithium on their surfaces, the reason and process for this in about 1% of red giants (a Sun-like star) has remained a mystery. Furthermore, star evolution models predict that the Lithium must have been destroyed in the star’s hot plasma.
Deepak of the IIA and Prof David L Lambert of the University of Texas, who is also an Honorary Fellow of the IIA, have confirmed for the first time that all lithium-rich stars burn helium in their cores. They hypothesized in a paper published in the journal MNRAS that lithium production is related to the violent helium-core flash. IIA is a self-contained institute under the auspices of the department of science and technology (DST).
Deepak explained that approximately four decades ago, a red giant with an unusually high lithium abundance at its surface was discovered: “..In every other way, this red giant was composed normally. Initial studies of Lithium in red giants revealed that only about 1% of sun-like red giants had a lithium-enriched surface. The processes that resulted in a 100-fold or greater increase in the lithium abundance in this exceptional red giant, as well as the reason for this selective enrichment of Lithium in the 1% of red giants, remain unanswered “
According to the DST, the authors drew on an extensive survey of the compositions of red giants conducted in Australia at the Australian National University and observations made with the 3.9m Anglo-Australian Telescope at the Australian Astrophysical Observatory.
“GALAH—named after a common Australian bird—collected approximately 5 lakh stars with well-defined physical and chemical properties, including lithium abundances. To determine whether Lithium enrichment in red giants is favored by a particular mass and metallicity range, they divided GALAH’s stars into different mass and metallicity ranges and then searched for Lithium-rich giants within these groups. “According to the DST.
This study, which is the first of its kind on this scale and across such a broad range of mass and metallicity, reveals the infrequent presence of lithium-rich giants in all Sun-like low-mass stars.
The researchers created virtual stars with varying masses and metallicities and compared their properties to real stars from the GALAH survey. These comparisons established that all lithium-rich stars have a core that burns helium.
Separately, researchers combined data on star interior oscillations with their lithium abundances to determine the origin of Lithium-rich giant stars. For this study, the DST said, they collected asteroseismic data, or information about oscillations in the interiors of giant stars with known lithium abundances.
“We discovered that all lithium-rich giant stars burn helium in their cores,” the researchers stated, adding that years ago, nuclear physicists proposed a simple and brief sequence of nuclear reactions involving a collision between two stable helium isotopes that resulted in the formation of a stable lithium isotope.
“This reaction is thought to occur during the initial violent ignition of helium-burning in the hydrogen-depleted core, just before the red giant’s stable helium burning. The authors adopt this position and invite theoretical astrophysicists interested in the interior structure of red giants to provide quantitative estimates of lithium production during helium burning ignition in red giants “the DST has been added.
Scientists from Indian Institute of Astrophysics (IIA) provide robust observational evidence for the first time that lithium (Li) production is common among low mass Sun-like stars during their He-core burning phase@IndiaDST
— PIB India (@PIB_India) July 7, 2020
Read: https://t.co/NLOktNvvtZ
Scientists from the Indian Institute of Astrophysics (IIA) have provided evidence for the first time that Lithium (Li) production is common among low mass Sun-like stars during their Helium (He) core burning phase. pic.twitter.com/Mj50XZhBjK
— Astha Sharma (@astha_sharma__) July 9, 2020
