The globular cluster NGC 6397 contains around 400,000 stars and is located about 7,200 light years away in the southern constellation Ara. With an estimated age of 13.5 billion years, it is likely among the first objects of the Galaxy to form after the Big Bang.
Credit: European Southern Observatory
A process similar to a conveyor belt transports heavy elements from the surface of stars into their interiors where they are destroyed, new observations suggest.
The findings, detailed in the Aug. 9 issue of the journal Nature, support the idea that the abundance of heavy elements in stars decreases with time and could help solve the cosmological lithium problem, a riddle that has been puzzling astronomers for years.
Lithium is one of the few elements thought to have been produced during the Big Bang, but when astronomers compare the amounts of lithium contained within the atmospheres of the very old stars in our Milky Way galaxy, they find their predictions are higher by a factor of 2 to 3.
Researchers trying to resolve this problem used the European Southern Observatory's Very Large Telescope in Chile to study a globular cluster containing half a million ancient stars called NGC 6397, located 7,200 light-years from Earth. The stars varied in age and were at different stages in their evolution.
The researchers found that as the stars age, the proportion of lithium in their atmospheres first slightly increases and then drops off sharply. The process is thought to take billions of years.
The researchers extrapolated backwards in time to determine what the stars' original lithium content was and found that the value was in good agreement with that predicted by Big Bang theory.
"The cosmological lithium discrepancy is thus largely removed," said study team member Andreas Korn of the Uppsala Astronomical Observatory in Sweden.
Scientists think that that stellar rotation and internal gravity waves are among the physical mechanisms contributing to lithium destruction, but more studies are needed to confirm this.
"The ball is now in the camp of theoreticians," Korn said.
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