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• First interstellar X rays detected
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Stars and other celestial objects radiate energy in many wavelengths other than visible light, which is only one small part of the electromagnetic spectrum. At the low end (with wavelengths longer than visible light) are low-energy infrared radiation and radio waves. At the high end of the spectrum (wavelengths shorter than visible light) are high-energy ultraviolet radiation, X rays, and gamma rays.

X-ray astronomy is a relatively new scientific field focusing on celestial objects that emit X rays. Such objects include stars, galaxies, quasars, pulsars, and black holes.

Earth's atmosphere filters out most X rays. This is fortunate for humans and other life on Earth since a large dose of X rays would be deadly. On the other hand, this fact makes it difficult for scientists to...