Congratulations to Andrea Socci on his successful PhD defense!

Congratulations to Andrea Socci on his successful PhD defense!

Delving into the fibers of star formation

Stars were the first astronomical objects known to humans. We can look up at the sky and see them everywhere. However, understanding the details of how they come to be is still a pressing question in current astronomical research. Stars form inside gigantic clouds of gas that, as we now know from state-of-the-art observations of the Milky Way, contain filaments of dust and gas. These structures permeate the interstellar medium of our galaxy, influencing—if not entirely driving—star formation. Dr. Andrea Socci investigated the role that these filaments play in the formation of new stars in our Galaxy.

Previous research on nearby clouds showed that, despite the fact that filaments exist in a variety of environments, they display a surprisingly typical width of 0.1 pc*. This characteristic scale would imply common initial conditions for star formation, which in turn would pose a challenge for current theoretical models. Recent observations with single-dish telescopes and interferometers have revealed a filamentary substructure within these filaments, thereby challenging the idea of a typical width for such objects.

Andrea used the homogeneous EMERGE Early ALMA Survey of the nearest high-mass star-forming cloud, Orion, to investigate this in depth. He identified a widespread presence of these small-scale fibers across the sample. His results show that fibers appear to trace the organization of dense gas at sub-parsec scales and drive star formation within each of these regions. Their widths vary by a factor of two across the sample. This systematic variation is induced by the density regime and the environmental conditions present in each region.

Andrea also explored the effects of the environment on these fibers, particularly the influence of cosmic rays. Cosmic rays are energetic charged particles that induce ionization within dense molecular gas. This, in turn, affects gas heating, its coupling to the magnetic field, and its chemical evolution. By adopting new implementations of previous analytical methods, along with newly developed approaches, he investigated the cosmic-ray ionization rate at parsec scales across a filament in Orion and across a filamentary dark cloud. In both cases, he found that the ionization rate varies throughout the region for three main reasons: attenuation as a function of column density, as predicted by theoretical models; local enhancements due to protostars; and overall attenuation induced by the magnetic-field morphology.

The combined study of filament properties and their interaction with the cosmic-ray ionization rate is an important step toward a more complete understanding of star formation. Andrea plans to continue his research on this fascinating topic.

I was not expecting to take part in a PhD program in Vienna. Looking back now, I am glad I did. Despite all the mishaps along the way, I truly enjoyed my time in this beautiful city and my day-to-day work at the institute. I am beyond grateful for all the experiences I had, all the things I learned, and, above all, all the people I met during these 4 and a half years of my life.

*Parsec – a unit used in astronomy to measure distances. One parsec is equal to 3.26 light-years.