Astronomers Detected COM’s In Young Starless Core L1521E For The First Time (Planetary Science)

Scibelli and colleagues, for the first time reported the discovery of complex organic molecules (COMs): dimethyl ether (CH3OCH3), methyl formate (HCOOCH3), and vinyl cyanide (CH2CHCN) in the young starless core L1521E. Their study recently appeared on journal Arxiv.

The chemistry of star and planet formation begins with the synthesis of molecules in interstellar molecular clouds. Dense (∼ 105 cm¯3 ) and cold (10 K) regions within these clouds, called starless and gravitationally bound prestellar cores, represent the earliest observable stage of low-mass (M ≤ few M) star-formation. It is during this phase prior to the formation of a first hydrostatic core (the foremost stage of a protostar), that the initial conditions for star and planet formation are set.

The discovery of COMs in prestellar cores leads to fundamental questions of how quickly these COMs form, and to what level of complexity. Thus, Scibelli and colleagues, in their recent paper targeted a dynamically and chemically young starless core in Taurus, Lynds 1521E (L1521E).

“The chemical and kinematical evidence agree that this object is one of the youngest starless cores known, with densities at > 105 cm¯3. Thus, L1521E is an excellent object toward which to test the limits of how quickly COMs form, to test what level of chemical complexity COMs form, and to test at what molecular abundances COMs form.”

— told Sciebelli, lead author of the study

They have searched for complex organic molecules (COMs) in the young starless core L1521E, and reported the first clear detection of dimethyl ether (CH3OCH3), methyl formate (HCOOCH3), and vinyl cyanide (CH2CHCN).

Figure 1. The chemical reactive desorption model used for L1521E is described as the ‘Minissale & Dulieu’ (MD) approach, where surface reactions dictate desorption efficiency. Their total (i.e., A + E states for CH3CHO) calculated abundances, with uncertainties, are plotted as horizontal lines that match the color-scheme of the modeled curves. © Scibelli et al.

They also detected eight transitions of acetaldehyde (CH3CHO), five of which (A states) were used to determine an excitation temperature to then calculate column densities for the other oxygen-bearing COMs. If source size was not taken into account (i.e., if filling fraction was assumed to be one), column density was underestimated, and thus they stress the need for higher resolution mapping data.

“The connection between L1521E, other starless and prestellar cores, low-mass hot cores and comets suggest that some COMs are seeded early on in the star formation process.”

told Sciebelli, lead author of the study

In addition, they calculated L1521E COM abundances and compared them to other stages of low-mass star formation, finding similarities to other starless/prestellar cores, suggesting related chemical evolution.

Moreover, they tested the scenario that assumes formation of COMs in gas-phase reactions between precursors formed on grains and then ejected to the cold gas via reactive desorption and found that it was unable to reproduce observed COM abundances, with the exception of CH3CHO.

These results suggested that COMs observed in cold gas are formed not by gas-phase reactions alone, but also through surface reactions on interstellar grains. Their observations presented a new, unique challenge for existing theoretical astrochemical models.

Featured image: Comparison of COM abundances at various stages of low-mass star formation, including prestellar cores, hot cores and comet © Scibelli et al.

Reference: Samantha Scibelli, Yancy Shirley, Anton Vasyunin, Ralf Launhardt, “Detection of Complex Organic Molecules in Young Starless Core L1521E”, ArXiv, pp. 1-15, 2021.

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