The Universe’s Lost Lithium

A decades-old clash between modern cosmology and stellar observations may have just gotten worse.

A paper set to appear in Physical Review Letters later this month might add to a problem that’s had astronomers baffled for 30 years: the universe doesn’t have enough lithium.

Cygnus X-1
An artist's highly symbolic representation of the Cygnus X-1 black hole and its X-ray-hot inner accretion disk. A new study suggests that jet-shooting, star-siphoning stellar mass black holes might make worse an already long-standing cosmochemical problem.
NASA / CXC / M.Weiss
As the third element in the periodic table, lithium is one of a few elements that have an abundance closely tied to processes just after the Big Bang. Detailed models of big bang nucleosynthesis predict certain levels of these elements, such as hydrogen and helium, and for the most part these models closely match what observers see in the cosmos.

But 30 years ago, Monique and François Spite (Paris Observatory) reported that the isotope lithium-7 was far rarer in old, metal-poor stars in the Milky Way’s halo than it should be. These stars formed in our galaxy’s early days, back when its chemical makeup more or less matched what existed after the universe’s birth. Relatively cool and with poor mixing between surface and interior, such stars should have lithium-7 levels in keeping with primordial abundances.

Yet these stars have at most one-third the amount of lithium-7 predicted. Even lower levels are found in the most primitive stars — stars with very low levels of heavy elements, which weren’t created by big bang nucleosynthesis. This upper limit became known as “the lithium problem.”

Astronomers have devised various solutions to explain the missing lithium, but nothing’s really worked. Any process that could deplete the lithium would need to happen in stars of various temperatures and compositions and without messing up the abundances of the other elements, François Spite says.

Now, Fabio Iocco (Oskar Klein Center for Cosmoparticle Physics, Sweden) and Miguel Pato (Munich Technical University, Germany) have added another potential hurdle: black holes.

Recent work suggests that in the early galaxy there may have been a fair number of “microquasars,” stellar-mass black holes yanking material off a stellar companion and shooting jets of superhot plasma into space. Iocco and Pato looked at the conditions in the hot accretion disks around these black holes, where temperatures can reach tens to hundreds of billions kelvin. Such temperatures jump over those where lithium-7 is merely disrupted (around 2.5 million K) and up to the point where the helium reactions that create lithium happen, Iocco says.

The duo found that, even if only 1% of the Milky Way’s microquasars produced temperatures hot enough to create lithium-7, the amount created would rival that expected from the universe’s first few hours.

So, the question remains: where is all the lithium?

7 thoughts on “The Universe’s Lost Lithium

  1. Rod

    The paper referenced at the start of this report was very interesting reading. Apparently in the Milky Way we may have some 10E+8 to 10E+9 stellar mass black holes that could be creating and adding to the Lithium problem. Over billions of years you would think this creates a larger 7Li abundance throughout the Milk Way and widen the BBN lithium problem. Perhaps a much shorter history of lithium production operating since the Milky Way formed is the solution as well as possible issues with BBN lithium production, thus the missing lithium is not missing, it was not there to begin with.

  2. Bruce

    When I first read this article I thought, Rod’s going to love this. Actually I like it too, but not for the problem it causes for the big bang theory. I like the finding that there is now a natural way for lithium to be replenished. Since Li is the first element to be fused in the core of a proto-star when fusion begins, without a recurring mechanism for Li production this useful element would become harder to come by in the very distant future. Therefore, this is not a “problem,” it’s a solution to a problem!

  3. Gordon

    The far out answer is all light matter is formed by ‘burning’ dark matter in black holes. It would also explain the lack of antimatter. Of course it is all a fairytail until we figure out how to make dark mater and can check it against the cosmic background.

  4. Rod

    Bruce, you thought correctly, I did very much enjoy this report. For your reading fun you can toss in the mix the matter vs. anti-matter problem in the big bang (we should not exist), the primordial neutrinos (too weak to detect with current equipment). So we get 3 here, BBN Li problem, matter vs. anti-matter production in big bang, and primordial neutrinos flooding the universe. Enjoy Bruce—Rod

  5. Bruce

    Rod: You’ll get no argument from me on this one; compared to stellar models, there’s much, much less observational support for the Big Bang Theory. (The theory, not the show 🙂
    Gordon: Intriguing suggestion. Does dark matter even fall into black holes? And if it does, could we detect it? Note the recent story about observations of galactic normal and dark matter decoupling in super cluster collisions.
    Grant: Another common use for Lithium (in the West) is pharmacologically as a treatment for bi-polar disorder. In the East they use herbs and long needles. I’m just saying … . (Note to all: this is NOT why I considered universal Li depletion to be a problem in need of solution!)

  6. ROGER


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