Chandra X-Ray Observatory
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Chandra X-Ray ObservatoryAn orbiting X-ray astronomy observatory launched by NASA in July 1999 as the third of its Great Observatories. Chandra, which takes its name from the 20th-century Indian-born US astrophysicist Subrahmanyan Chandrasekhar, was originally developed as one of the craft making up NASA's Advanced X-Ray Astrophysics Facility (see AXAF); dubbed AXAF-I and renamed after its launch, Chandra was equipped for high-resolution X-ray imaging and was deployed by the space shuttle Columbia into a highly eccentric orbit (apogee 140 161 km, inclination 28.5°) that has allowed long periods of observation unimpeded by Earth shadowing. Chandra's optics consist of four nested pairs of grazing incidence paraboloid and hyperboloid mirrors, each having an outer diameter of 1.2 meters and a focal length of 10 meters. With its Advanced Charged Couple Imaging Spectrometer (ACIS) and its high-resolution camera using large field-of-view microchannel plates to make X-ray images, Chandra's optical system achieves an angular resolution of 0.5 arcseconds over an operating range of 0.2–10 keV. Its high- and low-energy transmission gratings provide impressive spectral resolution throughout the range 0.09–10 keV.
Chandra has been called the most sophisticated X-ray observatory of its time, providing images of unprecedented detail at resolutions that are claimed to be about 50 times better than those achieved by ROSAT, the best X-ray astronomy satellite prior to 1999. In its first five years, Chandra has begun to penetrate the hottest, most energetic regions of the Universe. In particular, it has advanced our knowledge of black holes, discovering among many other things how fast they spin, finding evidence of a star torn apart by a black hole, and emphatically confirming the reality of the event horizon. It has revealed enormous tracts of hot gas, billions of parsecs distant and radiating at temperatures of tens of millions of degrees K. It has provided startling new images of supernova remnants such as the Crab Nebula, with its restless pulsar, showing intricate details never suspected before. It has made new studies of star-forming regions such as the Orion Nebula and analyzed the effects of galaxy collisions and the merging of galaxy clusters. Most notably, it has gathered direct evidence of dark energy and the expansion of the Universe.