High-energy phenomena refer to events and processes in the universe that involve extremely high energy levels, often far beyond what can be produced or studied in a laboratory on Earth. These phenomena can include the explosive death of massive stars (supernovae), the collision of neutron stars, the activity of supermassive black holes, and the acceleration of particles to near the speed of light in astrophysical environments such as cosmic rays and gamma-ray bursts. Studying high-energy phenomena can provide insights into the fundamental physics of the universe, the nature of extreme environments, and the processes that drive the evolution of galaxies and other cosmic structures. Researchers use a variety of observational techniques, including telescopes that detect gamma rays, X-rays, and high-energy particles, to study these phenomena and better understand their underlying mechanisms.