What explains the threefold lithium-7 deficit in old halo stars?
In plain words
Old metal-poor stars in the Milky Way halo show a constant lithium level, but it is about three times below the Big Bang prediction. Either the stars destroyed lithium, or the early universe made less of it.
Precise statement
Standard BBN with the Planck baryon density $\eta \sim 6.1 \times 10^{-10}$ predicts $\mathrm{Li}/\mathrm{H} \sim 5 \times 10^{-10}$, while the Spite plateau of metal-poor dwarfs ($[\mathrm{Fe}/\mathrm{H}] < -1.5$) gives $\mathrm{Li}/\mathrm{H} \sim 1.6 \times 10^{-10}$, a factor 3 to 4 at more than $5\,\sigma$. Identify the cause: stellar depletion by atomic diffusion and mixing, nuclear-rate errors, or non-standard physics (decaying particles, varying constants).
What would settle it
A measurement of unprocessed lithium, or a validated stellar model reproducing the plateau from the BBN value.
Status in the literature
Unverified note: it names recent work and was partly written without a live literature search; it awaits a check by an editor.
2024 to 2025 work favors stellar depletion and finds nuclear-rate solutions negligible, but no quantitative stellar model is established.
Problems built on this one
Special cases
- Can stellar transport deplete lithium uniformly by a factor three? · open
- What is the lithium abundance in gas never processed by stars? · open
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