Beyond the first galaxies primordial black holes shine

Understand

The presence of nine candidate galaxies at $z=17$ and $z=25$ discovered by the James Webb Space Telescope in relatively small sky areas, if confirmed, is virtually impossible to reconcile with the predictions of the current galaxy formation model.

• We show here that the implied UV luminosity density can be produced by a population of primordial black holes (PBHs) of mass $M_{\rm PBH} = 10^{4-5} \, M_{\odot}$ residing in low-mass halos ($M_h \approx 10^{7} \, M_{\odot}$), and accreting at a moderate fraction of the Eddington luminosity, $\lambda_E \simeq 0.36$.
• These sources precede the first significant episodes of cosmic star formation.
• At later times, as star formation is ignited, PBH emission becomes comparable to, or subdominant with respect to, the galactic emission.