On the Hunt For Rare Molecules in Stellar Nurseries (Cosmology)

The great sensitivity of the 30-meter Iram radio telescope allows it to detect very weak emissions, such as that from rare molecules such as HCNH +. A group of astronomers led by INAF studied this molecule (abundant in Titan’s atmosphere) in detail and for the first time it was clarified that the abundance of HCNH + is different depending on whether they are young star-forming regions ( cold) or evolved (hot). Details on A&A

Using the 30-meter Spanish Iram radio telescope, five researchers led by the National Institute of Astrophysics (INAF) have completed the first survey in star-forming regions of a rare but important interstellar molecule: HCNH + or protonated hydrogen cyanide . It is an ionized particle, one of the most abundant so far found in the atmosphere of Titan (the largest natural satellite of the planet Saturn). Experts believe that the HCNH + molecule is a crucial species in astrochemical reactions, but it has so far only been identified in a handful of star-forming regions, and therefore its chemistry is poorly understood. The team led by INAF hasobserved 26 large mass targets in different evolutionary stages, detecting the molecule in 16 regions. This represents the largest sample of sources in which this molecular ion has been found to date. The results are presented in an article recently published in the journal Astronomy & Astrophysics .

We interviewed the first author of the study, Francesco Fontani , an astronomer at the INAF in Florence and an adjunct professor of physics of the interstellar medium at the University of Florence. His research field mainly concerns the formation of stars and the presence in space of molecules of biological importance that can be linked to the origin of life in the Universe.

What is the HCNH + molecule and where can it be found?

«In Italian, the molecule is protonated hydrogen cyanide . On Earth it is not a compound that can be used because it is extremely unstable: if present in the atmosphere, due to the high density of the gas it would react almost instantly with something else forming a more stable compound. But in the rarefied, low-pressure gas of an interstellar cloud, where interactions between particles are much rarer, it can survive for a long time and be seen with radio telescopes. Other similar molecules (H3 +, N2H +, C3 +) are “interstellar” rather than terrestrial, because they survive for a long time only in that type of environment. HCNH + is probably the most abundant ionized particle in the atmosphere of Titan, the only satellite in the Solar System with an atmosphere, and also richer in nitrogen than Earth’s ».

Why is it an important molecule to study in interstellar space?

” It is thought to be a key species for chemical processes in the regions where stars form and is the major” progenitor “of the molecules HCN (hydrogen cyanide) and HNC (hydrogen isocyanide), two molecules very abundant everywhere in space and both involved in various synthesis theories of prebiotic molecules. In fact, it seems that from the polymerization of HCN it is possible to reach adenine, the nitrogenous base of Dna and Rna. In general, it is believed that HCNH + is a key molecule in interstellar chemical processes involving nitriles, organic compounds characterized by the functional group -CN (carbon-nitrogen), important in astrochemistry and astrobiology because they are possible progenitors of organic acids “.

What is the novelty of your studio compared to the state of the art?

“In our work we publish the detection of the emission of HCNH + in 16 regions or clusters in which stars of great mass are formed, that is 8-10 times the Sun large. The 16 regions have various” ages “: ranging from very young objects , cold and quiescent, in which the star formation process is at the beginning, to objects in more advanced stages, hot and turbulent. This allows us to study the major processes that form (and destroy) HCNH + under very different conditions. It is also the first study in which we compare the abundance of HCNH + in regions with very different physical and evolutionary properties, and for the first time we analyze the main chemical reactions related to HCNH + in a hot and evolved environment, while previous studies had focused only on cold and young environments ».

Francesco Fontani, researcher at the Arcetri (FI) Astrophysical Observatory of the National Institute of Astrophysics © INAF

What did you find out?

« The most important observational result is that HCNH + is significantly more abundant in the young phases of star formation, thus constituting an important reservoir of HCN and HNC already from these first moments. It has been seen ch the progenitors of the HCNH + molecule are different in gases with different physical and evolutionary conditions, and it is the first time that we realize this. Entering a bit into the technical, in young and cold regions (10 K, about -260 degrees Celsius), the “parents” are mainly the HCN + and HNC + ions; in more evolved and warm regions (relatively … we always talk about 30 K, or about -240 degrees Celsius) the parents are mainly HCN and HCO +. We found that the abundances of HCNH + relative to H2, the major interstellar molecule, are higher in cold regions than in warm ones, and this also has another interesting consequence: the abundance of HCNH + can be used to understand whether a region whose developmental age is not well known is “younger or older”. Molecules with these properties are also calledchemical clocks or chemical evolutionary indicators “.

Was the molecule studied by chance while you were looking for something else? What in particular?

“Yes, we were looking for molecules containing deuterium, the stable isotope of hydrogen with a proton and a neutron in the nucleus, following the idea that the abundance of these molecules changes with the physical and chemical evolution of the region that contains them. These observations have already been published , and have actually confirmed our hypothesis, which is that some molecules containing deuterium are indicators of the age of the host region. But sifting through the entire spectral band observed also showed the emission of many other molecules, including HCNH +, which we did not expect to be another indicator of age! ».

What are we left to discover about HCNH +?

“On the basis of our results we have understood for the first time what are the chemical processes that” on average “are dominant in forming HCNH + in regions, let’s say, colder and younger or warmer and more evolved, thanks to a big leap in terms of number and properties of the observed regions compared to previous studies (from 5-6 to 16 regions). In the future, we will need to observe even more regions with different physical properties to arrive at a full understanding of the role of this molecule in the important context of interstellar nitrile chemistry. ‘

Featured image: The molecular cloud G034.43 + 00.24, one of the targets of the study by Fontani et al. (2021), seen in the multi-band images of Glimpse (Benjamin et al. 2003), the infrared survey of the inner part of the Milky Way obtained with the Spitzer space telescope (red = 8 micrometers; green = 5.8 micrometers; blue = 4.5 micrometers ). The dark infrared filament, made up of cold, dense material, is filled with molecules (including HCNH +) that emit light at radio wavelengths. Credits: Ashley Thomas Barnes and Francesco Fontani


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