Star clusters as cosmic ray accelerators

TL;DR

Star clusters, through their energetic winds and supernovae, create superbubbles that serve as efficient environments for particle acceleration, potentially explaining the origin of high-energy cosmic rays and their observed properties.

Contribution

This paper highlights the role of star clusters and superbubbles as significant cosmic ray accelerators, offering insights into their contribution to Galactic cosmic ray flux and composition.

Findings

Star clusters generate superbubbles with turbulent gas motions.

Superbubbles are efficient sites for particle acceleration.

This mechanism may explain cosmic rays in the PeV range.

Abstract

Massive stars blow powerful winds and eventually explode as supernovae. By doing so, they inject energy and momentum in the circumstellar medium, which is pushed away from the star and piles up to form a dense and expanding shell of gas. The effect is larger when many massive stars are grouped together in bound clusters or associations. Large cavities form around clusters as a result of the stellar feedback on the ambient medium. They are called superbubbles and are characterised by the presence of turbulent and supersonic gas motions. This makes star clusters ideal environments for particle acceleration, and potential contributors to the observed Galactic cosmic ray intensity. The acceleration of particles at star clusters and in their surroundings may provide a major contribution to the observed CR flux. Moreover, it may explain the fine structures observed in the chemical composition of these particles, and possibly provide a solution to the puzzle of the origin of cosmic rays of energies in the PeV range and beyond.