A black hole is an invisible object with such powerful gravitational force that not even light can escape its surface. An X ray's energy depends on the energy of its source, so astronomers can use information gathered by the detectors to determine the temperatures of the various sources. Because the atmosphere absorbs X rays approaching the earth from cosmic sources, scientists use devices mounted on spacecraft to detect the rays. Characteristics of X rays Wavelength. X rays have longer wavelengths than gamma rays and shorter wavelengths than ultraviolet rays.
Scientists working in different fields define the ranges of wavelength differently.
By comparison, the wavelengths of visible light range from about 400 to 700 nm. Some scientists refer to X rays with wavelengths shorter than 0.1 nm as hard X rays because of their great penetrating power. Longer X rays are known as soft X rays. Many scientists who use X rays in their work measure wavelengths in angstrom units. One angstrom unit equals 0.1 nanometer.