Asteroids Crashing Into Dead Stars are Helping Explain Where the Universe’s Missing Lithium Went

What happened to all the lithium? The question has stumped astronomers for decades. While cosmologists have successfully predicted the abundance of the other light elements from the Big Bang, lithium has always come up short. Now, a team of astronomers may have found the reason: lithium-rich asteroids are smashing into white dwarves.

As amazing as it sounds, we can use nuclear theory to understand the conditions of the universe when it was only a dozen minutes old. In that inferno, the lightest elements – hydrogen, helium, and lithium – got their start. Astronomers have been able to compare the predicted abundances of those elements to what they see throughout the universe, and everything matches up…except lithium.

It’s called the “cosmological lithium problem” because that’s exactly what it is. We know that this story of the Big Bang is largely correct, so where did all the lithium do?

Wherever it is, it’s not in stars or interstellar gas clouds – we checked there.

And now a new survey by a team of astronomers with University of North Carolina Chapel Hill, University of Montreal and Los Alamos National Laboratory think they have the answer: white dwarves.

Using the Southern Astrophysical Research Telescope, the astronomers observed two very old white dwarf systems, whose planets formed over 9 billion years ago. Those planets are long gone, destroyed when their parent stars turned into white dwarfs.

But then pieces of those planets crashed into the white dwarfs, where the astronomers found signs of much more lithium than normal.

So potentially the missing lithium of the universe is bound up in planets and asteroids, and can only make itself visible to astronomers when those objects end up crashing into their parent stars. Only more observations will tell, and maybe we’ll finally find all that lithium.