Alcohol detected … in the center of our galaxy

Just walk through the door of a pharmacy or go to the do-it-yourself section of a supermarket to find isopropyl alcohol, also known as isopropanol. Used as a solvent, this colorless and flammable chemical compound is actually present in the formulations of a wide variety of products such as paints, waxes, varnishes or inks. It can also be used as an antiseptic or cleanser. But isopropyl alcohol can also be found a little further away than our local dealers: in the massive star-forming region of Sagittarius B2, located near the center of our Milky Way, for example.

For the first time, scientists have discovered this molecule in interstellar space, and more precisely in a molecular cloud whose chemical composition has been the subject of an in-depth study by astronomers for more than 15 years. Their goal: to understand how organic molecules are formed in the regions where new stars are born, and more specifically the relationship between the chemical composition of the interstellar medium and that of objects in the solar system such as comets that keep track of the conditions initials, which led to the formation of our planetary system.

A “birth room” of stars

“Sagittarius B2 (Sgr B2) is one of the largest massive star-forming regions – in terms of mass and rate of star formation – in our galaxy”details on Science and the Future Arnaud Belloche, an astronomer at the Max Planck Institute for Radio Astronomy in Bonn, who led the study. The large amount of matter (gas and dust grains) found in Sgr B2 makes it easier to detect molecules with low abundance, which would otherwise be difficult to spot in other less impressive star-forming regions, which has motivated a number of studies of the chemical composition of Sgr B2 since the 1970s. ”

Thanks to the high angular resolution and sensitivity of the ALMA telescope, located in the Atacama Desert in Chile, scientists are precisely able to determine in detail the chemical composition of the substance involved in the formation process. of stars and their associated planetary systems. Since 2014, ALMA observations have thus made it possible to identify three new organic molecules (that of isopropyl cyanide, N-methylformamide and urea) to which the molecule propanol has just been added (C3H7OH).

To to date, 277 molecules have been identified in the interstellar medium, “but the list increases regularly in relation to the discoveries”adds Arnaud Belloche. “The first three were identified in the 1930s-40s in the optical field, but almost all of the others have been identified thanks to the development of radio astronomy since the 1960s.” Isopropanol had not yet been observed. But in April 2022, a Spanish team announced that it had detected normal propanol via the radio telescope in Yebes, Spain, in a different part of the molecular cloud of Sgr B2 than the one being studied with ALMA. “When we also identified the normal propanol in the object we are studying with ALMA, we were able to determine for the first time the abundance ratio between these two isomers in the interstellar medium.”cheers the researcher.

One molecule, two versions

Normal propanol (or propan-1-ol or propyl alcohol) and isopropanol (or propan-2-ol or isopropyl alcohol) consist of the same atoms, but arranged differently. Thus, these two molecules are called “structural isomers” or “constitutional isomers”. The fact of having been able to observe these two different versions of propanol is a gift from god to scientists who are then able to determine the mechanism of formation of each. “Because the two molecules are very similar, they behave very similarly physically, which means they must be present in the same places and at the same times.”explains in a press release Rob Garrod from the University of Virginia, who was a co-signatory of the study published in Astronomy and astrophysics June 28, 2022.

Interstellar chemistry models contain a wide range of chemical reactions that have mostly not been characterized in the laboratory or by quantum chemical calculations. These models therefore contain a large number of uncertain parameters, which we test by comparing the results of these models with the amounts of the molecules that we measure in the interstellar medium, for example in Sgr B2 “adds Arnaud Belloche.

Understand the chemistry of the interstellar medium

A given molecule can only emit photons at very specific frequencies that are characteristic of its structure. These frequencies are known thanks to laboratory measurements performed by spectroscopists who have compiled databases. That Cologne Database for Molecular Spectroscopy (CDMS) refers thus. ILe the spectrum of the electromagnetic radiation emitted by all the molecules in the gas contained in Sgr B2, the team led by Arnaud Belloche isolated many signals or spectral lines at multiple frequencies before comparing them with data collected in the laboratory.

“The exploration of comets has shown us that they have a very rich chemical composition, even including, for example, glycine, the simplest amino acid (which has not yet been identified in the interstellar medium)”, concludes Arnaud Belloche. Many amino acids, the building blocks of the proteins that are characteristic of life on Earth, have also been identified in meteorites that have fallen to Earth. “We do not yet know what conditions were necessary for the production of all these molecules in the parent bodies of comets and meteorites. Were these conditions specific to the environment of the solar system when it was formed? Or can such a rich chemistry be expected to develop equally in all star-forming regions of our galaxy (and other galaxies)? “ A better understanding of the chemical processes operating in these environments could therefore provide some answers.

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