An Alternate Pathway for H$_2$ Formation in the Early Universe: A physical process to account for the presence and coevolution of the luminous galaxies and supermassive black holes at the high redshifts

Abstract

Molecular hydrogen (H$_2$) and hydrogen deuteride (HD) are key coolants in primordial gas and regulate the formation of the first stars and proto-galaxies. Recent results from the James Webb Space Telescope provide striking insights into galaxies detected at high redshifts, which are found to be significantly more abundant and luminous than expected from galaxy formation models, thus suggesting a gap in our understanding of the early Universe. Standard pathways for H$_2$ formation in the early Universe proceed through the H$^-$ and H$_2^+$ intermediates, both of which are strongly suppressed at high redshift by the cosmic microwave background. We propose an additional pathway for H2 and HD formation that could be active as early as the end of the epoch of recombination and could enable the formation of the first stars earlier than the current prediction at redshift z ~ 30 - 20. The proposed pathway relies on the manifestation of Jahn-Teller dynamical coupling between electronic states of H$_3^+$. This coupling induces transient three-body recombination in H$^+$, H and H, and charge exchange within the charged atom-dimer complex that directly creates ground-state H$_2$ (and HD), bypassing the fragile intermediates that limit the standard primordial pathways. Our analysis shows that this mechanism could occur under the thermodynamic conditions of the post-recombination epoch, also suggesting that it might be playing a role in the active galactic nuclei feedback processes, regulating the formation rates of the first stars and the accretion rates of the first black holes. Though the global impact on galaxy formation and black-hole growth is not yet determined and will require quantitative assessment in future modeling, the mechanism offers an additional chemical route for H$_2$ and HD formation, with substantial cosmological relevance for primordial chemistry and early structure formation.