A new study of an old sink of sulfur in hot molecular cores: the sulfur residue

TL;DR

This study investigates the sulfur depletion mystery in star-forming regions by modeling sulfur chemistry in hot cores, revealing that the sulfur residue accounts for only a small fraction of the missing sulfur.

Contribution

It incorporates recent experimental and theoretical data into a chemical model to explore the sulfur sink in dense star-forming regions, advancing understanding of sulfur chemistry.

Findings

Sulfur residue accounts for about 6% of sulfur in the model.

Most sulfur remains unaccounted for in solid or gas phases.

The model aligns with observed abundances of sulfur-bearing species.

Abstract

Sulfur appears to be depleted by an order of magnitude or more from its elemental abundance in star-forming regions. In the last few years, numerous observations and experiments have been performed in order to to understand the reasons behind this depletion without providing a satisfactory explanation of the sulfur chemistry towards high-mass star-forming cores. Several sulfur-bearing molecules have been observed in these regions, and yet none are abundant enough to make up the gas-phase deficit. Where, then, does this hidden sulfur reside? This paper represents a step forward in our understanding of the interactions among the various S-bearing species. We have incorporated recent experimental and theoretical data into a chemical model of a hot molecular core in order to see whether they give any indication of the identity of the sulfur sink in these dense regions. Despite our model producing reasonable agreement with both solid-phase and gas-phase abundances of many sulfur-bearing species, we find that the sulfur residue detected in recent experiments takes up only ~6 per cent of the available sulfur in our simulations, rather than dominating the sulfur budget.