Cosmic rays and molecular clouds

TL;DR

This paper explores how cosmic rays penetrate molecular clouds, produce gamma rays through interactions, and how gamma-ray observations can help locate cosmic-ray sources and understand their diffusion in the galaxy.

Contribution

It analyzes cosmic-ray interactions with molecular clouds and discusses how gamma-ray emissions can be used to identify cosmic-ray sources and study their diffusion properties.

Findings

Molecular clouds can be gamma-ray sources due to cosmic-ray interactions.

Gamma-ray observations help locate cosmic-ray accelerators.

Diffusion properties influence cosmic-ray overdensity around sources.

Abstract

This paper deals with the cosmic-ray penetration into molecular clouds and with the related gamma--ray emission. High energy cosmic rays interact with the dense gas and produce neutral pions which in turn decay into two gamma rays. This makes molecular clouds potential sources of gamma rays, especially if they are located in the vicinity of a powerful accelerator that injects cosmic rays in the interstellar medium. The amplitude and duration in time of the cosmic--ray overdensity around a given source depend on how quickly cosmic rays diffuse in the turbulent galactic magnetic field. For these reasons, gamma-ray observations of molecular clouds can be used both to locate the sources of cosmic rays and to constrain the properties of cosmic-ray diffusion in the Galaxy.