The James Webb begins to observe organic molecules in galactic nuclei

The Oxford University-led research is the first of its kind to study small dust molecules in the nuclear region of active galaxies using early James Webb observations .

The James Webb Space Telescope  has revealed new information about galactic formation and evolution by observing small organic molecules in the nuclear region of active galaxies.

Tiny dusty molecules known as polycyclic aromatic hydrocarbons (PAHs) are among the most widespread organic molecules in the universe and are important astronomical tools. For example, they are considered fundamental components 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 local physical conditions.

In search of clues to life

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

Surprisingly, the results reversed those of previous studies that had predicted that PAH molecules would be destroyed in the vicinity of 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 very energetic photons could potentially rip them apart. One possible reason could be that the molecules are shielded by large amounts of molecular gas in the nuclear region.

However, even where PAH molecules survived, the results showed that supermassive black holes at the heart of galaxies had a significant impact on their properties. In particular, the proportion of larger, neutral molecules increased, indicating that more fragile, smaller, and charged PAH molecules may have been destroyed. This brings severe limitations to the use of these PAH molecules to investigate how quickly an active galaxy produces new stars.

“This research is of great interest to the astronomical community in general, in particular to those who focus on the formation of planets and stars in the most distant and faintest galaxies,” Garcia-Bernete said in a statement.

“It is amazing to think that we can observe PAH molecules in the nuclear region of a galaxy and 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 properties are.” in the nuclear region. Such knowledge is key to using PAHs as an accurate tool for characterizing the amount of star formation in galaxies, and thus how galaxies evolve over time.”