Abstract: Very-high-energy (VHE) gamma-ray astrophysics has emerged as an exciting and vital field, with major discoveries made through experiments in space and on the ground. In space, the Fermi gamma-ray telescope studies some of the most violent processes in the Universe, and explores nature's highest energy accelerators. At even higher energies, gamma-ray astronomy can be carried out using ground-based telescopes, which detect the flashes of blue light from air-showers caused by gamma rays impacting the upper atmosphere. Some of the most exciting sources detected at very high energies are blazars, with relativistic jets, and Galactic sources including supernova remnants, pulsar wind nebulae, and binary systems. Gamma-ray production in all these sources occurs due to particle acceleration in extreme conditions of gravitational or magnetic fields, implying the existence of shocks and cataclysmic explosions. Gamma-ray astronomy works synergistically with the study of ultra high energy cosmic rays and observation of the Universe with the elusive high-energy neutrino. Multi-messenger astronomy has emerged as one of the most effective ways to observe the Universe.  

This talk will outline the scientific motivation for VHE gamma-ray astronomy, describe the techniques involved, and survey the astrophysics of the extreme Universe, as revealed by observations made with gamma rays. We will also describe future prospects with the state-of-the-art Cherenkov Telescope Array Observatory (CTAO), an international project of the next generation in ground-based astronomy. CTAO will have unprecedented sensitivity, will unravel the mysteries behind cosmic particles, supermassive black holes and explore dark matter, and will possibly bring us to the edge of the unknown.