Scientists have discovered a previously unknown space molecule while studying a relatively nearby region of intense star birth, a cosmic spot about 5,550 light-years away. It is part of the Cat’s Paw Nebula, also known as NGC 6334.
The team, led by Zachary Fried, a graduate student at the Massachusetts Institute of Technology (MIT), examined a section of the nebula known as NGC 6334I with the Atacama Large Millimeter/submillimeter Array (ALMA). This revealed the presence of a complex molecule known as 2-methoxyethanol, which had never before been seen in the natural world, although its properties had been simulated in laboratories on Earth.
The discovery of the molecule 2-methoxyethanol was extraordinary. It contains 13 atoms, which may not seem like a lot, but only six molecules with more atoms than this have been discovered in space. This molecule also represents the largest and most complex “methoxy” molecule found in space so far, referring to a chemical with a methyl group atom bonded to an oxygen atom.
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“Our group seeks to understand which molecules are present in the regions of space where stars and solar systems will eventually take shape,” Fried said. “This allows us to reconstruct how chemistry evolves along with the formation process of stars and planets.”
Interestingly, the same team also looked for 2-methoxyethanol in another region of space called IRAS 16293-2422B, home to four newborn protostars located in the Rho Ophiuchi star-forming region which is located about 359 light-years from we. This could suggest greater diversity in the chemical composition of star-forming regions.
ALMA knew what to look for in Cat’s Paw
Fried and colleagues did not undertake the investigation of NGC 6334I and IRAS 16293-2422B without any basis. They already had a good idea of the molecule they would look for with ALMA, an array of 66 radio telescopes located in the Atacama Desert in northern Chile. Basically, they received a hint from machine learning models that suggested they look for 2-methoxyethanol.
The team then measured and analyzed the rotational spectrum of 2-methoxyethanol on Earth, which Fried described as “the unique patterns of light they emit as they fall into space.”
“These patterns are fingerprints or barcodes for molecules,” the MIT researcher added. “To detect new molecules in space, we first have to have an idea of what molecule we want to look for, then we can record its spectrum in the laboratory here on Earth, and finally we search for that spectrum in space using telescopes.
“The barcode matches!”
“Ultimately, we observed 25 rotational lines of 2-methoxyethanol that aligned with the molecular signal observed toward NGC 6334I, thus resulting in a confident detection of 2-methoxyethanol in this source,” Fried said.
This successful detection then allowed the team to derive the physical parameters of the molecule alongside NGC 6334I, including the abundances in which it exists and the excitation temperature of the molecule.
“It also allowed us to investigate possible chemical formation pathways from known interstellar precursors,” Fried added.
Discoveries like this allow scientists to better understand how increasingly complex molecules emerge as stars form, as well as when planets begin to coalesce around those stars.
“Continuous observations of large molecules and subsequent derivations of their abundances allow us to improve our knowledge of how efficiently large molecules can form and by which specific reactions they can be produced,” Fried concluded. “Furthermore, since we detected this molecule in NGC 6334I but not in IRAS 16293-2422B, we were given a unique opportunity to examine how the different physical conditions of these two sources might influence the chemistry that may occur.”
The team’s research was published April 12 in the journal The Astrophysical Journal Letters.