How do cosmic-ray collisions produce gamma rays?

In the context of physics, cosmic-ray collisions produce high-energy gamma rays primarily through the production and subsequent decay of neutral pions.1

When primary cosmic-ray atomic nuclei collide with interstellar matter—specifically hydrogen—the interaction generates charged and neutral mesons, such as pions. While charged pions eventually decay into muons, electrons, positrons, and neutrinos, the neutral pions are unstable and decay very quickly into high-energy gamma rays.1

These gamma rays serve as a key indicator for astronomers, as surveys conducted by satellites show that cosmic rays are highly concentrated within the disk of the Milky Way Galaxy, with the measured intensity of these gamma rays aligning with theoretical calculations.1