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In astronomy, an emission process in molecular clouds whereby certain spectral lines in the microwave emission of particular molecules are strongly amplified by natural processes similar to those exploited in lasers. Maser action in an astronomical source was first discovered in 1965 in the emission from hydroxyl (OH) molecules in a source in the Orion Nebula. Other molecules subsequently found to show a similar effect include water (H2O), silicon monoxide (SiO), formaldehyde (H2CO) and methyl alcohol (CH3OH). The word "maser" is an acronym for "microwave amplification by the stimulated emission of radiation". See also: OH source. |