Polycyclic aromatic hydrocarbons (PAHs) are important carriers of organic matter throughout the universe. As organic molecules, they play a central role in interstellar chemistry and are closely related to the origin of prebiotic molecules. Understanding how these organic compounds evolve in molecular clouds—the cold, dark cradles of star formation—is essential for tracing the origins of complex molecules that may lead to life.

In this context, Dr. GE Jixing from the Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences and his collaborators have made new progress in uncovering the chemical behavior of PAHs in molecular clouds at different evolutionary stages. Their findings were recently published in Astronomy & Astrophysics.

The researchers compiled 39 molecular cloud samples with rich observational molecular species. They constructed an astrochemical model incorporating PAHs and systematically investigated the role of PAHs at different evolutionary stages of molecular clouds by comparing and analyzing the observed molecular abundances with the model results.

Their results suggest that the model incorporating PAHs improves the agreement with observed molecular abundances in most molecular cloud samples. Including PAHs has a minimal impact on the best-fitted chemical ages. 

Additionally, the study establishes the applicability of the best-fitted chemical ages for estimating the kinematic ages of molecular clouds.

This work provides a list of molecules that can indicate the presence of PAHs in molecular clouds, offering an important scientific basis for future observations and predictions.

The agreements between model and the sample。Black--without PAHs；cyan- with PAHs. The upper and lower panels are for the models with low (L) and high (H) metal initial abundances to the models respectively. (Image by XAO)

The correlation between the fitted chemical age and gas density by fitting the sample. The black, cyan and red dashed lines are for the fitted results from the models without, with PAHs and the combined sample of the former two. (Image by XAO)