Astronomers identify four lithium-rich giant stars in Small Magellanic Cloud

Astronomers have found four low-mass lithium-rich giant stars in the Small Magellanic Cloud, a nearby dwarf galaxy, according to a preprint led by Alessio Mucciarelli. The team observed 209 red giant branch stars with the FLAMES spectrograph on the Very Large Telescope in Chile, measuring how much lithium each star's atmosphere contains. Because lithium is destroyed at relatively low stellar temperatures, stars that still show strong lithium lines are unusual and can reveal how light elements are made and mixed in galaxies beyond the Milky Way.

The evidence rests on spectroscopic measurements of the lithium resonance line in red giants near the tip of the red giant branch. About one-third of the 209 stars showed a lithium line detected above five standard deviations, while roughly half exceeded three standard deviations; the rest yielded only upper limits. The measured lithium abundances varied strongly from star to star. The authors argue this scatter can be explained by a mix of thermohaline mixing, a deep circulation that destroys lithium, and lithium enrichment from novae, exploding white dwarf systems, that became important earlier in the SMC's chemical history.

Lithium is fragile: Big Bang nucleosynthesis set its starting amount, but stars can create and destroy it, so its abundance traces galactic evolution. The Milky Way has many known lithium-rich giants, but finding them in the Small Magellanic Cloud tests whether the same processes operate in an environment with fewer heavy elements and lower star formation. The result fits a pattern in which novae contribute lithium earlier in such galaxies, while stellar mixing erases part of the record. Red giants near the tip can still carry usable chemical fingerprints, though separating stellar processing from galactic enrichment remains difficult.

The next step is to compare these four stars with larger samples across the Magellanic Clouds and the Milky Way, especially stars with better age, mass and chemical composition estimates. Stronger evidence would come from follow-up spectroscopy that confirms the lithium detections, tracks whether the stars remain lithium-rich over time, and tests thermohaline mixing models against stars of different masses. The current study is limited by its focus on the brightest red giants and by incomplete detections, so the four lithium-rich giants are a promising clue rather than a settled answer.