An X-ray source is an object, or a location in the celestial sphere from which X-rays are detected. The term X-ray source avoids interpretation (i.e., any declaration what kind of object is producing the X-rays), though it is often used even when a certain type of source is assumed. X-ray astronomy began in full with the development of X-ray space observatories.
Shock and magnetic fields can be factors in producing the heat to produce discernible X-ray thermal emission. Stars (e.g., the Sun) produce X-rays, such as that from the corona which includes plasma significantly hotter than the stellar surface. X-ray is found from some pre-main-sequence stars, some early stars, and some cool stars such as M dwarves and brown dwarfs.