New research from MIT Professor Brett McGuire’s group has revealed the presence of a previously unknown molecule in space. The team’s open-access paper, “Rotational spectrum and first interstellar detection of 2-methoxyethanol using ALMA observations of NGC 6334I,” appears in the April 12 issue of Letters from the Astrophysical Journal.
Zachary TP Fried, a graduate student in McGuire’s group and lead author of the paper, worked to piece together a puzzle of pieces collected from around the world, stretching beyond MIT to France, Florida, Virginia and Copenhagen, to arrive at this exciting discovery.
“Our group is trying to understand what molecules are present in the regions of space where stars and solar systems will form,” Fried says. “This allows us to understand how chemistry evolves alongside the process of star and planet formation. We do this by observing the spin spectra of molecules, the unique patterns of light they emit as they tumble through space. These patterns are the fingerprints (barcodes) of the molecules. To detect new molecules in space, we first need to have an idea of the molecule we want to look for, then we can record its spectrum in the lab here on Earth, and then finally we search for that spectrum in space using telescopes.”
Searching for molecules in space
The McGuire group recently began using machine learning to suggest good target molecules to look for. In 2023, one of those machine learning models suggested that researchers target a molecule known as 2-methoxyethanol.
“There are a number of methoxy molecules in space, such as dimethyl ether, methoxymethanol, ethyl ether, and methyl formate, but 2-methoxyethanol is thought to be the largest and most complex ever observed,” Fried says. To detect the molecule using radio telescope observations, the group first had to measure and analyze its rotational spectrum on Earth. The researchers combined experiments at the University of Lille (Lille, France), New College of Florida (Sarasota, Florida), and MIT’s McGuire Lab to measure this spectrum across a broad frequency band from microwaves to submillimeter waves (about 8 to 500 gigahertz).
Data from these measurements were used to search for the molecule using Atacama Large Millimeter/submillimeter Array (ALMA) observations in two separate star-forming regions: NGC 6334I and IRAS 16293-2422B. McGuire’s group analyzed these telescope observations alongside researchers from the National Radio Astronomy Observatory (Charlottesville, Virginia) and the University of Copenhagen, Denmark.
“We finally observed 25 rotation lines of 2-methoxyethanol that matched the observed molecular signal toward NGC 6334I (the barcode matched!), which allowed us to reliably detect 2-methoxyethanol in this source,” Fried explains. “This allowed us to infer physical parameters of the molecule toward NGC 6334I, such as its abundance and excitation temperature. It also allowed us to investigate possible chemical formation pathways from known interstellar precursors.”
Look forward to
Molecular discoveries like this help researchers better understand how molecular complexity develops in space during the star formation process. 2-Methoxyethanol, which contains 13 atoms, is quite large by interstellar standards—as of 2021, only six species larger than 13 atoms have been detected outside the solar system, many by McGuire’s group, and all of them exist as ringed structures.
“Continued observations of large molecules and subsequent derivations of their abundances allow us to deepen our knowledge of how efficiently large molecules can form and the specific reactions that can produce them,” Fried says. “In addition, because we detected this molecule in NGC 6334I but not in IRAS 16293-2422B, we had a unique opportunity to study how the different physical conditions of these two sources can affect the chemistry that can occur.”
Republished with permission from MIT News. Read the original article.
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