In a recent study published in the journal Physical Review Letters, a team of researchers from the University of Western Australia, the Italian National Institute for Astrophysics, and the University of Cambridge have shed new light on the role of cosmic-ray protons in exciting molecular hydrogen, a process that could have significant implications for understanding the energy dynamics of molecular clouds.
The research team, led by Marco Padovani and Daniele Galli, along with Corey T. Plowman, Liam H. Scarlett, Mark C. Zammit, Igor Bray, and Dmitry Vursa, focused on the impact of low-energy cosmic rays (with energies less than 1 GeV) on molecular clouds. While previous studies have extensively examined the role of supra-thermal electrons produced during ionization in exciting molecular hydrogen, the direct role of primary cosmic-ray nuclei, such as protons, has been largely overlooked.
The researchers introduced cross sections for proton impact on molecular hydrogen (H2), calculated using a sophisticated semi-classical implementation of the molecular convergent close-coupling method. Their findings revealed that proton-induced excitation of H2 is comparable in magnitude to that caused by electrons. This discovery suggests that protons play a more significant role in the energy dynamics of molecular clouds than previously thought.
The implications of this research are twofold. Firstly, it affects the estimate of the cosmic-ray ionization rate, which is typically derived from observations in the near-infrared domain. Accurate knowledge of the excitation processes is crucial for interpreting these observations and understanding the ionization rates in molecular clouds. Secondly, the findings impact the understanding of cosmic-ray-induced H2 ultraviolet luminescence, a phenomenon that could provide valuable insights into the energy processes occurring in these clouds.
To facilitate the incorporation of these findings into numerical models, the researchers also derived a new approximated analytical parameterization of the spectrum of secondary electrons. This parameterization can be easily integrated into existing numerical codes, enabling more accurate simulations of the energy dynamics in molecular clouds.
In summary, this study highlights the importance of considering proton-induced excitation of molecular hydrogen in the energy dynamics of molecular clouds. The findings have practical applications for the energy sector, particularly in the field of astrophysics and space science, where understanding the behavior of cosmic rays and their interactions with matter is crucial for developing new technologies and exploring the universe.
This article is based on research available at arXiv.