Scientists have discovered a hitherto unknown space particle while examining a region relatively close to condensed star birth, a cosmic speck about 5,550 light-years away. It is part of the Cat's Claw Nebula, also known as NGC 6334.
The team, led by Zachary Freed, a graduate student at the Massachusetts Institute of Technology (MIT), examined a section of the nebula known as NGC 6334I using 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 remarkable. 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 to date, referring to a chemical containing a methyl group atom bonded to an oxygen atom.
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“Our group is trying to understand molecules in the regions of space where stars and solar systems will eventually form,” Freed said. “This allows us to piece together how chemistry evolves along with the process of star and planet formation.”
Interestingly, the same team also searched for 2-methoxyethanol in another region of space called IRAS 16293-2422B, which is home to four newborn protostars located in the star-forming region of Rho Ophiuchi which is located about 359 light-years away from us. This may indicate more diversity in the chemical composition of star-forming regions.
Alma knew what to look for in a cat's claw
Fried and his colleagues investigated NGC 6334I and IRAS 16293-2422B without any basis. They already had a good idea which molecule they would be looking for using ALMA, an array of 66 radio telescopes located in the Atacama Desert in northern Chile. Essentially, they received advice from machine learning models suggesting they look for 2-methoxyethanol.
The group then measured and analyzed the rotational spectrum of 2-methoxyethanol on Earth, which Fried described as “the unique patterns of light it emits as it rolls around in space.”
“These patterns are fingerprints or barcodes of molecules,” the MIT researcher added. “To detect new molecules in space, we must first have an idea of the molecule we want to search for, then we can record its spectrum in the laboratory here on Earth, and then finally search for that spectrum in space using telescopes.
“Barcode matches!”
“Ultimately, we observed 25 spin lines of 2-methoxyethanol that aligned with the observed molecular signal toward NGC 6334I, leading to the safe detection of 2-methoxyethanol in this source,” Freed said.
This successful discovery allowed the team to extract physical parameters of the molecule in conjunction with NGC 6334I, including the abundance at which it exists and the excitation temperature of the molecule.
“It also enabled us to investigate possible chemical formation pathways from known stellar precursors,” Farid added.
Discoveries like this allow scientists to better understand how increasingly complex molecules appear during star formation, as well as when planets begin to cluster around those stars.
“Continued observations of macromolecules and subsequent derivations of their abundances allow us to advance our knowledge about how efficiently macromolecules form and by what specific reactions they can be produced,” Farid concluded. “In addition, because we detected this molecule in NGC 6334I but not in IRAS 16293-2422B, we have a unique opportunity to look at how the different physical conditions of these two sources affect the chemistry that could occur.”
The team's research was published April 12 in the journal Astrophysical Journal Letters.
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