The most powerful persistent accelerators in the Universe are jetted active galaxies. Blazars, galaxies whose jets are directed towards Earth, dominate the extragalactic γ-ray sky. Still, most of the highest-energy particle accelerators probably elude detection. These extreme blazars, whose radiated energy can peak beyond 10 TeV, are ideal targets to study particle acceleration and radiative processes, and may provide links to cosmic rays and astrophysical neutrinos. The growing number of extreme blazars observed at teraelectronvolt energies has been critical for the emergence of γ-ray cosmology, including measurements of the extragalactic background light, tight bounds on the intergalactic magnetic field, and constraints on exotic physics at energies inaccessible with human-made accelerators. Tremendous progress has been achieved over the past decade, which bodes well for the future, particularly with the deployment of the Cherenkov Telescope Array.

宇宙中最强大的持续加速器是喷射的活跃星系。银河系是喷流指向地球的星系，在银河系外的γ射线天空中占主导地位。尽管如此，大多数能量最高的粒子加速器仍可能无法进行检测。这些极端的爆炸物的辐射能量可以超过10 TeV，是研究粒子加速和辐射过程的理想目标，并且可以提供与宇宙射线和天体中微子的联系。在太电子能中观察到的极端blazar数量的增加对于γ射线宇宙学的出现至关重要，其中包括对银河外背景光的测量，银河系磁场的严格边界以及在人造无法获得的能量上对奇异物理的限制加速器。