Heavier hydrogen unveils secrets of protostars
doi:10.1038/nindia.2014.155 Published online 17 November 2014
By using computer-based models, researchers have thrown new light on the formation of ions and neutral molecules based on deuterium, the heavier isotope of hydrogen in outer space1. These deuterium-based ions and molecules are born in interstellar medium, the space between stars filled with gas and dust clouds.
Protostars are large masses of gaseous molecular cloud which evolve through various stages before giving birth to stars. Abundance of different chemical species can help distinguish these evolutionary stages. In fact, previous studies had hinted that the fraction of deuterium-based ions could be used to define different evolutionary stages of protostars.
To better understand how deuterium-based ions and molecules could be used to study the evolution of protostars, the researchers developed the computer models which simulated 6149 reactions involving 601 chemical species including deuterium. These models mimicked the chemical reactions that usually happen on dust grain surfaces in interstellar medium at around 10 Kelvins. The reacting atoms and molecules were mainly ionised and evaporated by cosmic rays.
The researchers found that the hydrogen deuteride (HD) molecules and deuterium molecules (D2) were the most abundant chemical species throughout the evolution of protostars. Cosmic rays evaporated these molecules to gas phase.
The gas-phase chemical species reached a steady state after one million years. These gas-phase molecules survived for another two hundred thousand years before depleting and leaving behind abundance of water, formaldehyde and methanol molecules.
In addition, the researchers calculated the infrared features of the deuterium-containing molecules usually observed to be trapped in interstellar ice. They say that these findings could assist future observational studies that will use infrared telescopes to locate such deuterium-based molecules in outer space.
1. Das, A. et al. Deuterium enrichment of the interstellar medium. New. Astron. 35,53-70 (2014)