Complex Organic Molecules Discovered in Protostar Shock Waves

Astronomers have detected complex organic molecules, including methanol, in the outflow from a Class 0 protostar. These molecules form in the shockwave environment where protostellar outflows collide with the interstellar medium. This discovery provides insight into the origins of carbon-based molecules essential for life.

Protostars accrue gas and release energy, even before hydrogen fusion begins. This energy comes from shocks on the protostar's surface caused by infalling gas. Protostars also emit high-speed gas streams called astrophysical jets. These jets remove excess angular momentum, allowing the protostars to continue growing. The jets create illuminated shocks in the interstellar medium.

These shock fronts concentrate energy and matter, facilitating rapid chemical reactions. Heat and pressure within these regions break apart some molecules and bind others together. This process creates complex molecules.

Researchers examined outflows from the Class 0 protostar IRAS 4B1, a binary star in the NGC 1333 star-forming region. They focused on the shocked areas where complex organic molecules are both created and destroyed. The study, published in *Astronomy and Astrophysics*, used data from the Northern Extended Millimeter Array (NOEMA).

The team reported the first detection of three complex organic molecules: acetonitrile (CH₃CN), acetaldehyde (CH₃CHO), and deuterated methanol (CH₂DOH). Acetonitrile is notable as a nitrogen-bearing molecule, which are relatively uncommon. Acetaldehyde is an oxygen-bearing molecule and a key component in carbon-oxygen chemistry. The presence of deuterated methanol suggests it formed in the pre-stellar phase, was locked in ice, and then released by shocks while remaining intact.

Different molecules were found in regions with varying temperatures and densities, indicating distinct formation pathways. Further observations of IRAS 4B1, similar to those conducted on L1157-B1, could reveal more complex organic molecules and provide a comprehensive chemical inventory of the outflow. This information will be crucial for understanding the formation and destruction processes of complex organic molecules and the dynamics of protostellar outflows.