On the probability of the extremely lensed $z$=6.2 Earendel source being a Population~III star

Abstract: The recent discovery of the extremely lensed Earendel object at $z=6.2$ is remarkable in that it is likely a single star or stellar multiple, observed within the first billion years of cosmic history. Depending on its mass, which is still uncertain but will soon be more tightly constrained with the James Webb Space Telescope, the Earendel star might even be a member of the first generation of stars, the so-called Population~III (Pop~III). By combining results from detailed cosmological simulations of the assembly of the first galaxies, including the enrichment of the pristine gas with heavy chemical elements, with assumptions on key stellar parameters, we quantify the probability that Earendel has indeed a Pop~III origin. We find that this probability is non-negligible throughout the mass range inferred for Earendel, specifically ranging from a few percent at the lower-mass end to near unity for some Pop~III initial mass function (IMF) models towards the high-mass end of the allowed range. For models that extend the metal-enriched IMF to $500$\,M$_\odot$, the likelihood of Earendel being a Pop~III star stays at the few to ten percent level. We discuss the implications of such a discovery for the overall endeavor to probe the hitherto so elusive first stars in the universe.