X-Ray Astronomy

Among the largest and most productive x-ray missions were Uhuru (1970), which catalogued 339 x-ray sources; Einstein (also known as HEAO-2, 1978-1981); and EXOSAT (1983-1986). In addition, there have been many smaller-scale observations.

The more recent missions, such as the German ROSAT (Röntgensatellit), launched in 1990, contain very sophisticated instrumentation, including detectors and grazing incidence telescopes, which can pinpoint the location of an x-ray source to very high accuracy, and take x-ray pictures to show the shape and distribution of the source. This is an important improvement over early missions, which often were not able to determine the exact location of the x-ray sources, making it difficult to correlate the source with an object that could be detected in another wavelength region.

Recent missions have also been able to measure the x-ray spectrum, or strength of the radiation in different energy bands. This allows the identification of particular elements in the source. ROSAT identified more than 50,000 x-ray sources during its survey phase, when it scanned the sky for six months. It also finally succeeded in detecting x rays from the Moon, nearly 30 years after the first attempt to do so.

NASA launched the Advanced X ray Astrophysics Facility (AXAF), named the Chandra X-ray Observatory. Designed with a resolution 25 times better than any preceding x-ray telescope, CXO passes around the earth in an elliptical orbit, studying black holes, supernovas, and dark matter and in an attempt to increase our understanding of the origin and evolution of the universe.