James Webb Space Telescope reveals new surprises about the galaxy’s organic molecules

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Tiny dust molecules known as polycyclic aromatic hydrocarbons (PAHs) are among the most common organic molecules in the universe and are important astronomical tools. For example, they are considered fundamental building blocks of prebiotic compounds, which may have played a key role in the origin of life. PAH molecules produce extremely bright emission bands in the infrared region when illuminated by stars, allowing astronomers not only to track star-forming activity, but also to use them as sensitive barometers of stars. local physical conditions.

This new analysis, led by Dr Ismael García-Bernete of the University of Oxford’s Department of Physics, used the JWST’s state-of-the-art instruments to characterize, for the first time, the properties of PAHs in the nuclear region of three luminous active galaxies . The study was based on spectroscopic data from the James Webb Space Telescope’s MIRI, which specifically measures light in the 5 to 28 micron wavelength range. The researchers then compared the observations to the theoretical predictions for these molecules.

Surprisingly, the results overturned those of previous studies that had predicted that PAH molecules would be destroyed near the black hole at the center of an active galaxy. Instead, the analysis revealed that PAH molecules can actually survive in this region, even where high-energy photons could potentially tear them apart. A potential reason could be that the molecules are shielded by large amounts of molecular gas in the nuclear region.

García-Bernete said: “The JWST MIRI gives us a fantastic opportunity to observe galaxies in a way that has simply not been possible until now. We were thrilled to discover that these organic molecules can actually survive in extremely harsh conditions. »

However, even where PAH molecules survived, the results showed that supermassive black holes at the hearts of galaxies had a significant impact on their properties. In particular, the proportion of larger and neutral molecules became more important, indicating that smaller and more fragile charged PAH molecules may have been destroyed. This severely limits the use of these PAH molecules to probe how quickly an active galaxy is creating new stars.

“This research is of great interest to the wider astronomical community, especially those focused on planet and star formation in the most distant and faint galaxies,” García-Bernete said. “It is amazing to think that we can observe PAH molecules in the nuclear region of a galaxy and that the next step is to analyze a larger sample of active galaxies with different properties. This will allow us to better understand how PAH molecules survive and what their specific properties are in the nuclear region. Such knowledge is essential for using PAHs as an accurate tool to characterize the amount of star formation in galaxies, and therefore, how galaxies evolve over time.

– This press release was originally published on the University of Oxford website

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