First detections of the key prebiotic molecule PO in star-forming regions

TL;DR

This study reports the first detection of the prebiotic molecule PO in star-forming regions, revealing its formation pathways and abundance ratios, which are crucial for understanding phosphorus chemistry in early star formation.

Contribution

It presents the first observational detection of PO in star-forming regions and models its formation and abundance, expanding knowledge of prebiotic chemistry in space.

Findings

PO detected in two star-forming regions W51 e1/e2 and W3(OH)

PO/PN abundance ratios are 1.8 and 3 respectively

Chemical model explains formation via gas-phase reactions and freeze-out processes

Abstract

Phosphorus is a crucial element in biochemistry, especially the P-O bond, which is key for the formation of the backbone of the deoxyribonucleic acid. So far, PO has only been detected towards the envelope of evolved stars, and never towards star-forming regions. We report the first detections of PO towards two massive star-forming regions, W51 e1/e2 and W3(OH), using data from the IRAM 30m telescope. PN has also been detected towards the two regions. The abundance ratio PO/PN is 1.8 and 3 for W51 and W3(OH), respectively. Our chemical model indicates that the two molecules are chemically related and are formed via gas-phase ion-molecule and neutral-neutral reactions during the cold collapse. The molecules freeze out onto grains at the end of the collapse and desorb during the warm-up phase once the temperature reaches 35 K. Similar abundances of the two species are expected during a period of 5x10^{4} yr at the early stages of the warm-up phase, when the temperature is in the range 35-90 K. The observed molecular abundances of 10^{-10} are predicted by the model if a relatively high initial abundance of 5x10^{-9} of depleted phosphorus is assumed.