The branch of astronomy that uses observations of emissions in the x-ray part of electromagnetic spectrum to study extraterrestrial sources such as stars, galaxies, and interstellar gas clouds.
The branch of astronomy that deals with X-ray radiation from various celestial sources, esp. binary stars.
The study of celestial objects by measurement of the x-rays they emit. Because the Earth's atmosphere absorbs x-rays, x-ray detectors are usually carried into space on satellites. X-rays are emitted by high-energy objects such as active galactic nuclei, supernova remnants, x-ray binary stars, neutron stars, and the regions around black holes. Objects which do not produce their own x-rays can reflect radiation from nearby stars, making it possible to study the objects using x-ray astronomy; one notable example of this is the analysis of solar x-rays reflected by the Moon.