doi:10.1038/nindia.2013.135 Published online 8 October 2013
Researchers have discovered that a low-mass protostar located in a nebula about 765 light years away (NGC 1333) has a low abundance of oxygen molecules . The finding assumes importance since previous observations and astronomical models have not detected or predicted the low abundance of molecular oxygen in the interstellar medium.
Oxygen is the third most abundant element in the Universe after hydrogen and helium. This makes oxygen very important for understanding the formation of astronomical objects and the subsequent evolution of their chemistry.
The researchers investigated the oxygen abundance of the interstellar medium by capturing images of a low-mass protostar in NGC 1333 (NGC 1333-IRAS 4A) using Herschel Space Observatory and employing computer-based astronomical models. A protostar is a cloud of interstellar gas and dust that gradually collapses to form a hot, dense core, which evolves into a star.
The researchers found that oxygen and hydrogen atoms on dust grains in the protostar react with each other, forming their molecular counterparts.
In a protostar, oxygen and hydrogen atoms hop between dust grains, and react with each other. Hydrogen atoms hop faster than oxygen atoms. Before they have the chance to form oxygen molecules, accreted oxygen atoms are hydrogenated, leading to the formation of hydroxyl radicals and water.
The results for IRAS 4A suggest that a long pre-collapse stage is a characteristic of the earliest stages of star formation. In this stage, both atomic and molecular oxygen are frozen out of the dust grains and are converted to water ice. The model results also indicate that the fraction of molecular oxygen in the gas and on the grains must be very small indeed.