From nanoparticles to macromolecules

The constituents of the cosmic nanoworld are small enough to exhibit characteristics reminiscent of molecules. At the same time, they are large enough to have properties typical of solid state materials. This hybrid nature of macromolecules and nanoparticles attracted the attention of EU-funded scientists.

Within the NANOCOSMOS (The cosmic nanoworld astrophysics at the interface between the molecular and the macroscopic) project, the scientists modelled the effects of photon irradiation on dust nanoparticles. The same modelling approach was used for amorphous carbon nanoparticles and polycyclic aromatic hydrocarbons (PAHs).

The absorption and scattering of photons is the root source of the decreasing light intensity and the shift of observable wavelengths of light from distant stars. Modelling work confirms that understanding these phenomena necessitates an accounting of the structure of nanoparticles.

While carbon nanoparticles have a 3D structure where carbon atoms are arranged in hexagonal rings with different orientations, PAHs are characterised by a single layer of such rings fused together. Among the implications for astronomical observations, the scientists focused on the mid-infrared emission of galaxies.

Infrared observations from satellites indicate the presence of stochastically heated nanodust and PAHs. Their dissociation as a result of differences in the intense radiation they are exposed to could explain the variations found in the mid-infrared spectra of distant galaxies.

Thanks to their peculiar structure, C60 and C70 – the largest molecules known to exist in space and to date the only polyaromatic molecules detected in space – could also contribute to the mid-infrared emission of galaxies. Their stability against collisions with ions was, therefore, studied under the harsh conditions experienced in the interstellar medium.

Both C60 and C70 belong to the class of molecules termed fullerenes, after architect Buckminster Fuller. Like every molecule in space, they absorb infrared light at a unique set of wavelengths. Nonetheless, when tested, they were proven to be rather stable and resistant to radiation.

The NANOCOSMOS results are expected to open new paths for the study of ever-more-complex interstellar medium constituents as well as the evolution of nanoparticles during supernova explosions. Moreover, scientists could also determine the impact of nanoparticle evolution in the stellar remnants around old stars.