Have metal-free Population III stars been observed? · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
Have metal-free Population III stars been observed?
Plain
The very first stars formed from pure hydrogen and helium and are predicted to have been very massive and short-lived. No such star system has been confirmed, though JWST has found candidates.
Precise · changed · core
Revision 1: Identify a stellar system with gas metallicity below the critical value $Z_{\mathrm{crit}}$ (theoretical range about $1e-6\ \text{to}\ 1e-3.5\ Z_{\mathrm{sun}}$), strong $\mathrm{He}\ \mathrm{II}\ 1640\ \text{Angstrom}$ emission and no detected metal lines, consistent with a top-heavy initial mass function. The leading candidate is LAP1 at $z \sim 6.6$, lensed by the cluster MACS J0416. An answer is a confirmed detection with metal-line upper limits below $Z_{\mathrm{crit}}$, or a measured upper bound on the Population III star-formation rate density at $z > 6$.
Revision 2: Identify a stellar system with gas metallicity below the critical value $Z_{\mathrm{crit}}$ (theoretical range about $10^{-6}\ \text{to}\ 1e-3.5\ Z_{\mathrm{sun}}$), strong $\mathrm{He}\ \mathrm{II}\ 1640\ \text{Angstrom}$ emission and no detected metal lines, consistent with a top-heavy initial mass function. The leading candidate is LAP1 at $z \sim 6.6$, lensed by the cluster MACS J0416. An answer is a confirmed detection with metal-line upper limits below $Z_{\mathrm{crit}}$, or a measured upper bound on the Population III star-formation rate density at $z > 6$.
Settled by
Deep JWST spectroscopy of lensed candidates reaching metal-line limits below $Z_{\mathrm{crit}}$ together with He II equivalent widths.
Kind
well-posed
Answer type
yes-no
References
(empty)
Literature status
open
Status note
Visbal, Hazlett and Bryan (2025, arXiv:2508.03842) argue that LAP1-B matches three theoretical Population III predictions; confirmation is pending.
Posed since
(empty)

Decisions