Primordial Black Holes Proposed as Explanation for Lithium-7 Abundance Discrepancy
Researchers have proposed that primordial black holes could resolve the cosmological 'lithium problem' by evaporating baryons that convert excess lithium-7 into helium-4 via neutron capture. Big Bang nucleosynthesis theory predicts roughly three times more lithium-7 than is actually observed in ancient stars, a discrepancy that has persisted for decades. If confirmed, this mechanism would simultaneously provide evidence for primordial black holes and resolve one of the outstanding puzzles in standard cosmology.
A paper published in the European Physical Journal C proposes that primordial black holes (PBHs) could explain why the observed abundance of lithium-7 in old, metal-poor stars is significantly lower than what standard Big Bang nucleosynthesis (BBN) theory predicts. The mechanism relies on baryons evaporated by PBHs through Hawking radiation interacting with lithium-7 nuclei via neutron capture, producing unstable lithium-8 or beryllium-8 intermediates that rapidly decay into pairs of helium-4 nuclei. The authors show quantitatively that this process can reduce the lithium-7 fraction relative to total baryon number density down to the observed value. The lithium problem has been an open question in cosmology since the 1980s, with proposed solutions ranging from stellar depletion mechanisms to new physics beyond the Standard Model. This PBH-based explanation is notable because it invokes a well-motivated class of dark matter candidates and does not require modifications to the core BBN framework. The paper was submitted to arXiv in June 2026 and published in Eur. Phys. J. C 85 (2025).
What different sources said
- arXiv astro-phCenter
Possible explanation of primordial $^7$Li deficit
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