Mystery of missing lithium extends beyond Milky Way

Stars in the Milky Way appear to be missing some of the element lithium, and new observations of a distant star cluster confirm that the problem isn’t unique to our galaxy. The missing lithium confounds astronomers because it may require rethinking ideas about how stars operate or what conditions were like in the early universe (SN: 8/9/14, p. 6).

In the first three minutes after the Big Bang, the universe created mostly hydrogen and helium with a smattering of lithium. Observations of hydrogen and helium in the early universe match theoretical predictions. But there’s only about a third as much lithium in the atmospheres of old stars as there should be.

Until now, most of those lithium measurements were made in stars born in the Milky Way. To see if the problem extended beyond our galaxy, astronomers turned the Very Large Telescope in Chile towards old stars in Messier 54, a star cluster roughly 90,000 light-years away in the constellation Sagittarius. M54 is part of a tiny galaxy being cannibalized by the Milky Way. The observations, appearing online September 9 in the Monthly Notices of the Royal Astronomical Society, show that stars in M54 have just as little lithium as stars native to the Milky Way, suggesting that the lithium problem is universal.