What is X-ray sources

X-ray sources sources of x-radiation from outside the solar system. Some 100 sources within the galaxy have been observed as objects that emit most of their energy in the x-ray region of the electromagnetic spectrum and only a relatively small proportion of their energy in the visible spectrum. Many of these x-ray sources appear to be members of a binary system, consisting of one optically visible star and one very compact object; it is thought that the latter is either a *neutron star or (if very massive) a *black hole. Owing to the absorption of x-rays by the earth's atmosphere these x-ray sources are only visible by x-ray telescopes carried by space probes and satellites, although some high-energy x-rays can penetrate the upper atmosphere and are detectable by x-ray telescopes mounted on balloons.