Probably all of us have had direct experience with the chemical molecule iso-propanol, as it has numerous practical applications including those of an antiseptic, solvent, and cleaning agent.
However, this material is not only present on Earth; scientists working under the direction of Arnaud Belloche from the Max Planck Institute for Radio Astronomy in Bonn have recently discovered the molecule for the first time in interstellar space.
It was discovered in the huge star-forming area Sagittarius B2, which is close to the Milky Way’s center and is known as a “delivery room” of stars. The ALMA telescope in the Chilean Atacama Desert is being used to learn as much as possible about the molecular cloud’s chemical makeup.
For for than 50 years, scientists have been looking for molecules in space. 276 molecules have been discovered in the interstellar medium so far, according to researchers.
Many research organizations have provided spectroscopic data to the Cologne Database for Molecular Spectroscopy (CDMS), which is used to identify these substances and has frequently been successful in doing so.
The purpose of the current research is to comprehend the formation of organic molecules in the interstellar medium, particularly in areas where new stars are formed, and the potential complexity of these molecules.
The main goal is to find links between the chemical makeup of objects in the solar system, like comets, as the Rosetta mission did with comet Churyumov-Gerasimenko a few years ago.
Sagittarius B2 (Sgr B2) is a prominent star-forming region in our Galaxy that is close to the renowned source Sgr A*, the supermassive black hole in the galaxy’s center, and where several molecules have been previously found.
According to Arnaud Belloche, the principal investigator on the detection report and director of the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany, “our group began to investigate the chemical composition of Sgr B2 more than 15 years ago with the IRAM 30-m telescope. These observations were successful and led in particular to the first interstellar detection of several organic molecules, among many other results.”
Since the Atacama Large Millimeter/submillimeter Array (ALMA) was established ten years ago, it has become possible to observe Sgr B2 with more precision than was previously possible with a single-dish telescope.
This has allowed for the long-term study of Sgr B2’s chemical composition, which has benefited from ALMA’s high angular resolution and sensitivity.
Since 2014, three new chemical substances have been discovered as a result of ALMA observations (iso-propyl cyanide, N-methylformamide, and urea). ALMA’s latest discovery is propanol (C3H7OH).
Since its detection in space, propanol has become the most abundant alcohol in the universe. This molecule has two different forms, or “isomers,” depending on which carbon atom the hydroxyl (OH) functional group is attached to: 1) normal-propanol, in which the OH group is attached to the last carbon atom in the chain, and 2) iso-propanol, in which the OH group is attached to the middle carbon atom in the chain.
On Earth, iso-propanol is also well known as the main component of hand sanitizers. In the ALMA data set, the propanol in Sgr B2 was shown to exist in both isomers. The discovery of iso-propanol in the interstellar medium and the discovery of regular propanol in a star-forming region are both firsts.
Prior to the ALMA discovery, a Spanish research team using single-dish radio telescopes made the first interstellar detection of normal-propanol in a nearby molecular cloud to Sgr B2. But ALMA was the only instrument that could find isopropanol near Sgr B2.
“The detection of both isomers of propanol is uniquely powerful in determining the formation mechanism of each. Because they resemble each other so much, they behave physically in very similar ways, meaning that the two molecules should be present in the same places at the same times,” adds Rob Garrod of the University of Virginia in Charlottesville, USA.
“The only open question is the exact amounts that are present – this makes their interstellar ratio far more precise than would be the case for other pairs of molecules. It also means that the chemical network can be tuned much more carefully to determine the mechanisms by which they form.”
Due to its high sensitivity, high angular resolution, and wide frequency coverage, the ALMA telescope network was needed to find both isomers of propanol near Sgr B2. Spectral confusion makes it hard to find organic molecules in the spectra of regions where stars are being made.
Each molecule emits radiation at particular frequencies that are known as its “spectral fingerprint” and may be measured in the lab.
“The bigger the molecule, the more spectral lines at different frequencies it produces.
In a source like Sgr B2,” according to Holger Müller from Cologne University, “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.”
Because ALMA has a high angular resolution, it was possible to find parts of Sgr B2 that emit very narrow spectral lines—five times narrower than the lines that the IRAM 30-m radio telescope found on larger scales. The ability to distinguish between the two isomers of propanol in Sgr B2 was largely due to the narrowness of these lines, which lessens spectral confusion.
The sensitivity of ALMA was also important; if it had been even slightly worse, it would not have been feasible to detect propanol in the data obtained.
This study is an ongoing effort to investigate the chemical makeup of the regions in Sgr B2 where new stars are forming in order to better understand the chemical processes involved in star formation. Determine the star-forming regions’ chemical make-up in order to maybe discover new interstellar chemicals.
According to Oliver Zingsheim, also from Cologne University, “Propanol has long been on our list of molecules to search for, but it is only thanks to the recent work done in our laboratory to characterize its rotational spectrum that we could identify its two isomers in a robust way.”
Researchers can probe particular components of the chemical reaction network that results in the production of closely related molecules in the interstellar medium, such as normal- and iso-propanol or, as was done in the past, normal- and iso-propyl cyanide, by detecting and measuring the abundance ratio of these molecules.
“There are still many unidentified spectral lines in the ALMA spectrum of Sgr B2 which means that still a lot of work is left to decipher its chemical composition,” adds Karl Menten, Director at the MPIfR and Head of its Millimeter and Submillimeter Astronomy research department.
“In the near future, the expansion of the ALMA instrumentation down to lower frequencies will likely help us,” according to the director, “to reduce the spectral confusion even further and possibly allow the identification of additional organic molecules in this spectacular source.”
Image Credit: Wikipedia
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