The Star That Should Not Exist
A faint star in the constellation of Leo, called SDSS J102915+172927, has been found to have the lowest amount of elements heavier than helium (what astronomers call “metals”) of all stars yet studied. It has a mass smaller than that of the Sun and is probably more than 13 billion years old.
This intriguing composition places it in the “forbidden zone” of a widely accepted theory of star formation, which predicts that stars like this, with low mass and extremely low quantities of metals, shouldn’t exist because the clouds of material from which they formed could never have condensed.
Also very surprising was the lack of lithium. Such an old star should have a composition similar to that of the Universe shortly after the Big Bang, with a few more metals in it. But the team found that the proportion of lithium in the star was at least fifty times less than expected in the material produced by the Big Bang.
Astronomers point out that this freakish star is probably not unique. They have identified several more candidate stars that might have metal levels similar to, or even lower than, those in SDSS J102915+172927.