Astronomers at the National Astronomical Observatory in China (NAOC) have discovered a star with an abnormally high lithium (Li) abundance. This is reported in the journal Nature Astronomy.
It is known that lithium is unable to exist for a long time in the deep layers of the atmosphere of stars due to the high temperature. As a result, this element should be present in very small quantities in heated red giants. However, in 1982, astronomers discovered the first red giant with a high lithium abundance, which contradicted existing models of stellar evolution. In the past three decades, only 150 such objects have been found, and only in three of them the prevalence of lithium (A) reaches 3.3 (A shows the ratio of the number of lithium atoms to the number of hydrogen atoms in a star relative to the Sun, expressed in a logarithmic scale).
Scientists have discovered the star TYC 429-2097-1, which has the highest lithium abundance of any known star (A = 4.51). It is about a thousand times higher than the standard values (A = 1.5).
It used to be thought that high levels of lithium were due to "pollution" from an external source, such as a Jupiter-class gas giant (or brown dwarf) that collided with a star, a less hot and young companion star, or the interstellar medium. However, the abnormally high metal content characteristic of TYC 429-2097-1 is inexplicable from this point of view, since external sources themselves have a limited supply of lithium. Only the star's own production of Li can resolve the paradox.
The synthesis of lithium in a star is due to the Cameron-Fowler mechanism, which is carried out through the synthesis of a beryllium atom (Be) from helium where the temperature is too high for lithium. As a result of convection, Be is carried to the surface, where it turns into lithium in colder conditions. However, this mechanism for giant stars requires additional mixing of layers. At the same time, the simulation results showed that it is this process that provides the observed level of lithium content for TYC 429-2097-1.