Hydrocarbon dust is one of the main types of dust found in interstellar space. It consists of complex molecules, including polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons. PAHs are compounds containing several benzene rings, while aliphatic hydrocarbons are compounds in which the carbon atoms are linked by chains or rings without benzene rings.

Scientists believe that hydrocarbon dust can change under the influence of radiation or shock waves in the interstellar medium, but the exact mechanisms of this process are still not fully understood.

To better understand how hydrocarbon dust is processed, a group of astrophysicists studied 138 galaxies that are actively forming stars and relatively close to us (less than 3 billion light-years away).

Scientists used data obtained with the AKARI space telescope, which allows studying objects in the infrared range. In particular, we analyzed the spectra of these galaxies in the wavelength range of 2.5 to 5 μm. These data made it possible to distinguish the brightnesses associated with aromatic and aliphatic components of hydrocarbon dust. Aromatic components emit light at a wavelength of 3.3 μm, and aliphatic at a wavelength of 3.4 to 3.6 μm.

The authors also used photometry data obtained with the help of the AKARI, WISE and IRAS telescopes to estimate the total infrared brightness (LIR) of these galaxies and the intensity of the radiation field in them.

The results showed that galaxies with higher total infrared luminosity tend to have a lower ratio between aliphatic and aromatic components. This may indicate that in such galaxies, aliphatic components decay faster than aromatic components.

Scientists also discovered that there is an inverse relationship between the luminosity ratios of aliphatic and aromatic components and the intensity of the radiation field. This means that in galaxies with a stronger radiation field, aliphatic components decay faster than in galaxies with a weaker radiation field. In addition, merging galaxies were found to have a lower aliphatic/aromatic luminosity ratio than other galaxies.

These results suggest that hydrocarbon dust is recycled under the influence of radiation and shock waves in the interstellar medium. In particular, aliphatic components, which are chemically less stable than aromatic ones, are destroyed faster in conditions of strong radiation fields and shock waves generated during the merger of galaxies.

This study helps to better understand the processes occurring in the interstellar medium and their impact on the evolution of galaxies. The results of the analysis may be useful for further research in astrophysics and cosmology, as well as for the development of more accurate models of the formation and evolution of galaxies.