Complex Organic Molecules (COMs) in Star-Forming Regions: A Virtual Special Issue

Abstract

RecommendationsT his virtual special issue is concerned mainly with a class of interstellar molecules that strongly resemble organic molecules present in the terrestrial organic laboratory.These molecules are known as "complex organic molecules", a term abbreviated either as COMs or iCOMs, with the "i" standing for "interstellar" , even though these molecules, containing from 6 to 13 atoms, are hardly complex when compared to much larger molecules found on Earth.The COMs, which include simple alcohols, esters, nitriles, and ethers, have been observed extensively by radio astronomy.These molecules were originally detected in star-forming regions known as "hot cores" or "hot corinos".The distinction depends upon the mass of the object, with the latter eventually becoming a solarlike system, while the former will give birth to more massive stars.Each consists of gas and dust collapsing toward a star in the formation known as a protostar.The hot-core gas, which possesses temperatures ranging from 100 to 300 K, is formed from earlier colder stages of portions of interstellar clouds, known as cold cores and pre-stellar cores, which heat up as they collapse, following an initial isothermal period.The collapsing hot-core material can lead to so-called protoplanetary disks in solar-like systems.These disks and the protostars that they surround are the precursors of new planetary systems.Consequently, the chemistry of these later stages of star formation is related to the initial inventory of organic molecules on newly formed planets and may be related to the origin of life.Although COMs were originally detected in hot-core gas, they have since been found in the gas phase of cold cores, prestellar cores, winds and shocks associated with the formation of disks, the disks themselves, and earlier stages of star formation, known as translucent clouds.The dominant mechanism for the formation of COMs in hot cores is thought to proceed in two steps.In the first step, hydrogenated species (including radicals) are produced on the surfaces of icy mantles of interstellar dust particles.In the second step, there are two possibilities: COMs can be formed (i) on the grain mantles as they gradually warm up during the process of star formation and/or (ii) in the gas phase when they sublimate at large enough grain temperatures (about ≥100 K).The reactions on the grain mantles are thought to be promoted by ultraviolet (UV) photons, which activate stable molecules into reactive radicals, which then associate to form COMs via diffusive chemistry on granular surfaces.As the temperature continues to increase, the COMs are released into the gas, where they are detected.Once other molecules trapped in the grain mantles Special Issue: Complex Organic Molecules (COMs) in Star-Forming Regions

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