Birth of the first stars amidst decaying and annihilating dark matter

TL;DR

This paper investigates how decaying and annihilating dark matter can influence the formation of the first stars by affecting molecular hydrogen cooling, potentially delaying or accelerating star formation and impacting early universe signals.

Contribution

It introduces a toy halo model to quantify dark matter energy injection effects on star formation thresholds, revealing both positive and negative feedback mechanisms.

Findings

Dark matter models can significantly alter star formation thresholds.

Energy injection can both delay and promote star formation.

Impacts on 21cm signals at cosmic dawn are possible.

Abstract

The first stars are expected to form through molecular-hydrogen (H$_2$) cooling, a channel that is especially sensitive to the thermal and ionization state of gas, and can thus act as a probe of exotic energy injection from decaying or annihilating dark matter (DM). Here, we use a toy halo model to study the impact of DM-sourced energy injection on the H$_2$ content of the first galaxies, and thus estimate the threshold mass required for a halo to form stars at high redshifts. We find that currently allowed DM models can significantly change this threshold, producing both positive and negative feedback. In some scenarios, the extra heating of the gas raises the halo mass required for collapse, whereas in others, energy injection lowers the threshold by increasing the free-electron fraction and catalyzing H$_2$ formation. The direction of the effect can be redshift-dependent. We also bracket the uncertainties from self-shielding of halos from Lyman-Werner radiation. Hence, exotic energy injection can both delay and accelerate the onset of star formation; we show how this can impact the timing of 21cm signals at cosmic dawn. We encourage detailed simulation follow-ups in the most promising regions of parameter space identified in this work.