High Quality Content by WIKIPEDIA articles! X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray emission from celestial objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray astronomy is part of space science. X-ray emission is expected in sources which contain an extremely hot gas at temperatures from a million to hundred million degrees kelvin. IN general, this occurs in objects where the atoms and/or electrons have a very high energy.