An “old” star could provide new information on the evolution of stars

A newly discovered star could challenge some models of how stars evolve and how they produce elements as they age.

All elements of the universe are formed within stars. As stars age, the composition of the elements they contain also changes. For example, it is widely believed that when stars burn, they lose lighter elements like lithium in exchange for heavier elements like carbon and oxygen.

But a new study, led by researchers at the University of Florida and including an astronomer at North Carolina State, examines a star that appears to be an exception. The study appears in The Astrophysics Journal.

This star, named J0524-0336, was discovered during a study to search for older stars in the Milky Way. It is an evolved star, meaning it is in the final stages of its “life” and is starting to become unstable. This also means that it is much larger and brighter than most other stars of its type, estimated to be around 30 times the size of the sun.

The researchers used spectroscopy, which uses wavelengths of light to measure the amounts of elements present in a star, and discovered an abundance of lithium in J0524-0336, which was unexpected in such an old star. .

“When our team first looked at the spectrum of this star in 2018, we thought there was an error in our data where we were going to detect lithium,” says Ian Roederer, associate professor of physics at NC State.

“But when I looked more closely at the data in 2019, I thought the original data might actually be correct, so I collected an additional spectrum from this star the following month and we confirmed that the signal was real.

“It was the strongest lithium signal I have ever seen in a star,” says Roederer. “The amount of lithium in this star far exceeds that of any other known star.”

The team came up with a few potential hypotheses to explain the high lithium content of J0524-0336. It could be that it is in a still unobserved phase of the evolutionary cycle of stars, or that it has acquired this element during a recent interaction with another celestial body.

Stars as old and large as this have been theorized to absorb nearby planets and neighboring stars as they age, so J0524-0336 may have simply detected another lithium-rich body and did not not yet merged the new material.

Rana Ezzeddine, a professor of astronomy at UF and co-author of the study, believes that with the amount of lithium found in J0524-0336, it is likely that both hypotheses could have contributed, but additional work is needed. necessary.

“If we see a buildup of dust in the star’s circumstellar disk, or the ring of debris and material ejected from the star, that would clearly indicate a mass loss event, such as a stellar interaction,” explains Ezzeddine.

“If we do not observe such a disk, we could conclude that lithium enrichment could occur due to a process, yet to be studied in detail, that takes place inside the star.”