Mystery of missing lithium extends beyond Milky Way

Nearby galaxy confirms conundrum is not limited to our neighborhood

Star cluster Messier 54

ELEMENT ENIGMA  Star cluster Messier 54, seen in an image from the Very Large Telescope, is low in lithium, just like stars in the 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.

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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