The cosmological lithium problem

Instituto Nacional de Pesquisas Espaciais, Av. dos Astronautas 1758 – Jardim da Granja, São José dos Campos, SP 12227–010, Brazil

^⋆ Corresponding author: oswaldo.miranda@inpe.br

Received: 11 March 2025
Accepted: 8 August 2025

Abstract

Context. The discrepancy between the predictions of primordial nucleosynthesis and the observed lithium abundance in Spite plateau stars has been attributed either to a challenge to the standard model of nucleosynthesis or to stellar processes occurring after the stars formed. To understand the origin of this discrepancy, it is crucial to link the cosmic star formation rate with a chemical enrichment model that incorporates the yields of both Population (Pop) III and II stars. It is within this framework that the evolution of lithium can be determined.

Aims. The primary goal is to demonstrate that there is no discrepancy between the predictions of primordial nucleosynthesis and the observed lithium abundance.

Methods. By combining a standard chemical evolution model with the hierarchical structure formation scenario, it is possible to determine the lithium abundance as a function of [Fe/H]. The model’s results are compared with observational data from extremely metal-poor stars, Spite plateau stars, Gaia-Enceladus sources, the Small Magellanic Cloud, lithium abundances in Solar System meteorites, and two extremely iron-poor stars: J0023+0307 and SMSS J0313–6708.

Results. The Spite plateau is naturally established in the range −8.0 ≲ [Fe/H]≲ − 2.0 with ⁷Li/H ∼1.81 × 10⁻¹⁰. We find that J0023+0307 could have formed ∼4.4 × 10⁵ − 1.3 × 10⁶ years after the explosion of the first Pop III star in the Universe, whereas for SMSS J0313–6708 this event would have occurred ∼2.2 × 10⁵ − 4.4 × 10⁵ years later.

Conclusions. The Spite plateau serves as an observational signature of the formation of Pop III stars. The abundances observed in J0023+0307 and SMSS J0313–6708 are consistent with Pop III progenitor stars in the mass range 10 − 100 M_⊙. However, if some high-redshift star formation occurs within subhalo-like structures, the contribution of stars in the mass range 140 − 260 M_⊙ to the formation of the extended Spite plateau cannot be ruled out.