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.
Good
agreement
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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