Astrophysical origins of ultra-high energy gamma-ray emissions

The Large High Altitude Air Shower Observatory (LHAASO), one of the key national scientific facilities of China, has ushered in the new era of ultra-high energy gamma-ray astronomy. As of now, it has discovered many important phenomena, providing us with critical clues to unravel the puzzle of the origin of Galactic cosmic rays and a unique tool to probe extreme physical processes in extreme astrophysical objects. This paper will describe the ultra-high energy gamma-ray sources detected by LHAASO, as well as the physical pictures of relevant astrophysical objects.