A French-Dutch team of astronomers, including Stéphanie Cazaux of the Kapteyn Astronomical Institute of the University of Groningen, has managed to prove with laboratory experiments that molecules on micron-sized dust particles in space can be converted directly into a gaseous state. This result can have important implications for theories on the chemical composition of the universe and the way stars are created. The findings have been published online in Nature Scientific Reports.
It had already become clear in the 1960s that in regions where stars and planets are formed, dust particles play an important part in the production of molecules found in the universe, ranging from simple to extremely complex. However, the precise mechanism that enabled molecules on the surface of dust particles to transform immediately into gas and be released into space remained unknown.
In order to investigate how the molecules on dust particles are converted into a gaseous state, the astronomers studied in the lab how water is formed on silicates. The researchers chose these minerals because they compare well to dust particles in space. Molecular oxygen was first deposited on the surface, which had been cooled to the extremely low temperature of -263 degrees Celsius (10 degrees above absolute zero). Hydrogen atoms were subsequently deposited on the same surface. Mass spectrometer measurements then showed that 90 percent of the water molecules that were created immediately left the surface and transformed into gas.
Although the process was already being incorporated in astrochemical models of formation, estimated values had to be used. The new, experimentally determined data now available will have consequences for star formation theory, since it is the chemical composition of a cloud that ‘collapses’ to form a star that determines the speed of star formation, the number of stars and their ultimate mass. Energy must to be released during the collapse and the chemical composition of the cloud plays a major role in this process. ‘Our experiments show that micron-sized dust particles in the universe have a direct impact on the chemistry of astrophysical objects’, says Cazaux. ‘This not only has major implications for the interpretation and analysis of many objects in the universe, but also for our understanding of star formation.’
The experiments were conducted at the LERMA lab of Cergy-Pontoise University in Paris.
More information: Dr Stéphanie Cazaux , Kapteyn Astronomical Institute, University of Groningen
Reference: Dulieu, F. et al. How micron-sized dust particles determine the chemistry of our Universe. Nature Scientific Reports
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