As Moby once said, "We are all made of stars" — all the elements heavier than hydrogen, helium and lithium were formed in the solar furnaces of the original stars before being spewed forth into the universe to create everything else. But a newly analyzed star in the Leo constellation has characteristics that shouldn't be possible — and will require us either to rethink what we know of the universe, or what we know of stars.
The more hydrogen, helium and lithium stars have in them, the older they are. Newer stars contain more metals produced by older suns, blasted throughout space from novas. This means that you can estimate a star's age based on its metal contents — except in the case of the star known as SDSS J102915+172927. It has a mass less than our sun, extremely low quantities of metals, and is probably more than 13 billion years old. According to our current models, it shouldn't be able form with that composition.
What's even weirder is that a star this old should contain mostly lithium. But its lithium levels are 50 times less than what they should be — and it contains an enormous amount of calcium instead. With a proportion of metals this low, it should be an extremely ancient star. And yet its composition doesn't match the theorized composition of the universe at its creation.
So what happened to the lithium? That's the big question right now. Either something odd has happened to this star, or we need to revise our understanding of what the early universe was like. Researchers have identified some other stars which might also have metal deposits this low, and they plan to investigate further, to unravel what made these "stars that should not exist" do exactly that.