Effects of stellar-mass primordial black holes on first star formation

TL;DR

This study uses simulations and models to assess how primordial black holes of about 30 solar masses influence early star formation, finding minimal impact on the initial star-forming processes but some effects on larger scale structure formation.

Contribution

It provides a self-consistent analysis of PBH effects on first star formation, combining perturbations and feedback, and evaluates their significance within observational constraints.

Findings

PBHs do not significantly alter first star formation in minihaloes.

PBHs may influence larger scale structure formation and halo mass distribution.

Lyman-Werner photons from PBHs could aid in direct-collapse black hole formation.

Abstract

We use cosmological hydrodynamic zoom-in simulations and semi-analytical models to study the effects of primordial black holes (PBHs) on first star formation. Our models self-consistently combine two competing effects: initial (isocurvature) perturbations induced by PBHs and BH accretion feedback. Focusing on PBHs with masses $\sim 30\ \rm M_{\odot}$, we find that the standard picture of first star formation in molecular-cooling minihaloes is not changed by PBHs, as the simulated star-forming gas clouds in the central parsec are very similar to those in the $\rm \Lambda CDM$ case when PBHs make up $f_{\rm PBH}\sim 10^{-4}-0.1$ of dark matter. With a dynamical friction timescale of $\sim 2-10\ \rm Myr$ when the central gas density reaches $10^{5}\ \rm cm^{-3}$, it is also unlikely that PBHs can sink into star-forming discs and affect the evolution of protostars, although they may interact with the stars during the main-sequence stage. At larger scales, PBHs tend to shift star formation to more massive haloes, and accelerate structure formation. The latter effect is stronger in regions with higher initial overdensities. For $f_{\rm PBH}\sim 10^{-4}-0.01$ (allowed by observational constraints), the collapsed mass fraction of haloes hosting Population III stars is similar (within a factor of $\sim2$ at $z\lesssim 30$) to that in $\rm \Lambda CDM$, implying that the impact of stellar-mass PBHs on the cosmic star formation history at $z\gtrsim 10$ is small. We also find that the Lyman-Werner photons from PBH accretion in atomic-cooling haloes may facilitate the formation of direct-collapse BHs.