There’s alcohol in space. No, these are not bottles of wine thrown away by careless astronauts; rather, it is in microscopic molecular form. Now, researchers believe they’ve discovered the largest alcohol molecule in space yet, in the form of propanol.
Propanol molecules exist in two forms, or isomers, both of which have been identified in observations: normal propanol, which was first detected in a star-forming region, and isopropanol (the key ingredient in hand sanitizer), which has never been seen in interstellar form before.
These discoveries should shed light on the formation of celestial bodies such as comets and stars.
“Detecting the two isomers of propanol is particularly powerful in determining the mechanism of formation of each,” says astrochemist Rob Garrod of the University of Virginia. “Because they look so similar, they physically behave very similarly, which means that both molecules should be present in the same places at the same time.”
“The only open question is the exact quantities that are present – this makes their interstellar ratio much more precise than would be the case for other pairs of molecules. It also means that the chemical lattice can be tuned much more carefully to determine the mechanisms by which they form.
These alcohol molecules were found in what is called a “birthing room” of stars, the gigantic star-forming region called Sagittarius B2 (Sgr B2). The region lies near the center of the Milky Way and close to Sagittarius A* (Sgr A*), the supermassive black hole around which our galaxy is built.
While this kind of deep space molecular analysis has been happening for more than 15 years, the arrival of the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile 10 years ago has increased the level of detail at which astronomers can access.
ALMA offers higher resolution and a higher level of sensitivity, allowing researchers to identify molecules that were not visible before. Being able to distinguish the specific radiation frequency emitted by each molecule in an occupied part of space like Sgr B2 is crucial to calculating what exists.
“The bigger the molecule, the more spectral lines it produces at different frequencies,” says physicist Holger Müller from the University of Cologne in Germany. “In a source like Sgr B2, there are so many molecules contributing to the observed radiation that their spectra overlap and it is difficult to disentangle their fingerprints and identify them individually.”
Thanks to the way ALMA can detect very narrow spectral lines, as well as laboratory work that comprehensively characterized the signatures that propanol isomers would give off in space, the discovery was made.
Finding closely related molecules – like normal-propanol and iso-propanol – and measuring their abundance relative to each other, allows scientists to look in more detail at the chemical reactions that produced them.
Work continues to discover more interstellar molecules in Sgr B2 and to understand the type of chemical melting pot that leads to star formation. The organic molecules isopropyl cyanide, N-methylformamide and urea have also been identified by ALMA.
“There are still many unidentified spectral lines in the ALMA spectrum of Sgr B2, which means that there is still a lot of work to be done to decipher its chemical composition,” says astronomer Karl Menten of the Max Planck Institute. of radio astronomy in Germany.
“In the near future, the expansion of ALMA instrumentation to lower frequencies will likely help us reduce spectral confusion even further and possibly allow the identification of additional organic molecules in this spectacular source.”
The research has been published in Astronomy & Astrophysics here and here.