Usually, the lithium content in stars decreases during evolution. With all this, astronomers have long encountered ancient luminaries with a high content of this metal. The new star turned out to be a record holder among its kind. Modern models cannot explain its composition.

With age, the lithium content in the photosphere of stars, i.e. in the lower atmosphere, decreases. In low-mass stars, this begins even before entering the main sequence, when thermonuclear reactions become their energy source. Moreover, the rate of decrease in lithium content cannot be explained by the standard maturation of the star. Obviously, internal hydrodynamic processes contribute.

Astronomers generally expect to see low lithium content in all low-mass red giants. Even more surprising are the mature stars that manage to retain high lithium content.

Red giants with abnormally high lithium content were first noticed in the 1980s. It is quite simple to think of lithium in cool stars, so a lot of observational data has accumulated over the past decades. On average, one to two percent of red giants have high contents of this element.

About 150 superlith giants are known today. Of these, about 20 are considered superlith stars with a relative metal content index above 3.3. Only a few giants have more than four.

Astronomers from the University of Florida (USA) have discovered an adult red giant J0524-0336 in the halo of the Milky Way with a lithium content index of about 5.62, making it the most superlithium-rich star known so far. The article was published in the journal Astrophysics Journal.

The star was detected as part of a search for old stars in the Galaxy. The giant J0524-0336 is approaching the final stages of its evolution and is becoming unstable. It is much larger and brighter than stars of its kind. As the authors of the study assume, its mass is approximately 0.8 solar masses, which is usually the case for such giants at this stage of development. It has now been revealed that it is about 30 times more massive than the Sun.

“We found that J0524-0336 has 100,000 times more lithium than the Sun at its current evolutionary stage. Such a number is difficult to explain with accepted stellar evolution models. Perhaps there is another mechanism for lithium production or retention,” explained Rana Ezzeddin, an astronomer at the University of Florida.

Several mechanisms are known that could explain the high lithium content in red giants. These mechanisms can be divided into external and internal. In a new scientific paper, scientists evaluated all the assumptions about the parameters of J0524-0336.

External mechanisms include planetary absorption and interaction with a companion star. To explain the high lithium content, the planet itself would need to have an abnormally high amount of the metal. Moreover, according to models, the probability of such stars forming planets is generally low. With a companion star, things are not so simple. Judging by the motion of the giant J0524-0336, it does not currently have a neighbor, but its very rapid rotation could indicate a recent interaction with another star.

The internal processes are more difficult to understand. Theoretically and according to observational data, at a certain stage of development, under suitable conditions, red giants can start producing lithium. This requires a strong stirring in the stars. Astronomers have not yet fully understood the mechanisms of this mixing.

There is another version. An extremely high lithium content can be observed due to the emergence of a temporary lithium shell. This is probably an unexplored stage in the development of red giants before the transition to more comfortable lithium production. According to calculations, it can last about 20 thousand years. This hypothetical stage is called lithium flash (lithium flashThe authors of the new paper suggested that J0524-0336 experienced such a “flare.”

“If we find a dust cluster in the disk around the star or a ring of debris and material ejected from the star, we will understand that the star has lost mass, for example, during an interaction with another star. If we do not see such a disk, we can conclude that lithium enrichment occurred due to an as yet unknown process inside the star,” concluded Rana Ezzeddin. Scientists plan to continue observing the star.