Which high-energy messengers can be produced by cosmic-ray interactions near black holes?

• A. Visible light only.
• B. Gamma rays and neutrinos.
• C. Gravitational waves only.
• D. Only radio waves.

Answer: (B)

When cosmic rays collide in the extreme environments around black holes, their interactions produce high-energy particles through hadronic processes. Collisions with ambient matter or photons create pions: neutral pions decay into gamma rays, while charged pions decay into muons and neutrinos. The neutrinos escape almost unhindered and carry information from deep in these regions, and the gamma rays travel outward as high-energy photons that we can detect with gamma-ray telescopes. Gravitational waves require large-scale, rapid mass motions such as black-hole mergers, not the microscopic particle interactions of cosmic rays; radio and visible light can arise from other processes (like synchrotron emission or thermal radiation), but they aren’t the direct high-energy messengers produced by these interactions. So the best answer is gamma rays and neutrinos.