A new study published in the Astronomical Journal, led by Assistant Professor of Astronomy Lana Ezzedine and University alumni Jeremy Koukavany with collaborators, reports the discovery of a star that may challenge astronomers’ understanding of stellar evolution and chemical element formation, and mark a new phase in the research growth cycle. It is widely accepted that as a star burns, lighter elements such as lithium are replaced by heavier elements such as carbon and oxygen. However, analysis of this new star reveals that its lithium content is not only high for its age, but also higher than normal levels for stars of any age. The star, named J0524-0336 after its spatial coordinates, was recently discovered by Ezzeddin as part of another study using a survey to look for older stars in the Milky Way galaxy. It is an evolved star, meaning it is in the later stages of its “life” and starting to become unstable. This also means it’s much larger and brighter than most other stars of its kind, with its mass estimated to be about 30 times that of the Sun. To measure J0524-0336’s elemental composition, Ezzeddine’s team used a method called spectroscopy. A spectroscope is attached to a telescope and filters the star’s light into individual rainbows. Dark spots in this spectrum can be used to determine how much of each element the star is made up of. “We found that J0524-0336 contains 100,000 times more lithium than the Sun at its current age,” Ezzeddine said. “This amount calls into question common models of star formation and may indicate a previously unknown mechanism for lithium production or storage within stars.” The team came up with several possible hypotheses to explain J0524-0336’s high lithium content. It could be in a previously unobserved phase of a stellar evolutionary cycle, or it could have acquired the element through a recent interaction with another object. Stars as old and massive as this one are thought to absorb nearby planets and neighboring stars as they age. Thus, J0524-0336 may have simply absorbed another lithium-rich object and never had a chance to fuse the material together. Ezzeddine believes that both hypotheses likely contributed, given the amount of lithium found in J0524-0336, but more work is needed to reach a conclusion. Ezzeddine, Kowkabany, now a graduate student at FSU, and their collaborators plan to conduct further research on J0524-0336. They plan to use a continuous monitoring program to track the changes in the star’s composition over time, observing at different wavelengths, including infrared and radio waves, to determine whether material is being ejected from the star. “If we detect dust accumulation in the star’s circumstellar disk, or in a ring of debris or material ejected from the star, this would be a clear indication of a mass-loss phenomenon such as a stellar interaction,” Ezzeddine explained. “If we do not observe such a disk, we can conclude that lithium enrichment is occurring instead, due to processes yet to be discovered in the star’s interior.”

source: https://phys.org/journals/astrophysical-journal/