Introduction
Launched with the Shuttle Columbia on July 23 1999 from CapeCanaveral, the Chandra X-ray Observatory is the first X-ray astronomy telescope that matches the /12 arcsecond imaging power, and the 0.1% spectral resolving power, of optical telescopes. (The previous best X-ray telescopes managed either 5 arcseconds [ROSAT], or 10% spectral resolution [ASCA].) Chandra achieves these improved characteristics through much improved X-ray mirrors. These mirrors are 'Wolter type I' mirrors, which reflect X-rays by having the X-rays come in at an angle of only 1 degree to the surface, hence the name 'grazing incidence' mirrors. A Wolter I mirror resembles a slightly tapered cylinder, with a slight parabolic curvature that reflects the X-ray light onto a second, hyperbolic, curve to form an image. Because the X-rays are only bent by a few degrees, the focus lies far from the mirror, 10 meters in the case of Chandra.
The fine angular resolution of the Chandra mirror images away the bright background glow of X-rays that had limited the sensitivity of earlier X-ray telescopes, enabling the detection of X-ray sources some 100 times fainter than before. In addition, many X-ray sources, such as supernova remnants and the hot gas in clusters of galaxies, are extended on the sky, and Chandra reveals their structure in great detail. The third advantage of a fine mirror, is that when the transmission gratings are used to disperse the X-rays into a spectrum, much finer detail can be seen.
Main Characteristics of the Chandra X-ray Observatory
- Operating: 23 July 1999 - present (March 2008). Could last through 2020.
- Band: 0.1-10kilovolt X-rays
- Angular resolution: 0.5 arcsec
- Spectral resolving power, R: 10 (ACIS CCDs); ~300 (HETGS, LETGS)
Instruments:
- X-ray mirror (1000 cm^2), 0.5 arcsecond Half Power Diameter (on-axis)
- X-ray diffraction gratings, 2: High Spectrometer (HETGS); Low Energy
Transmission Grating Spectrometer (LETGS):
- CCD imagers: Advanced CCD Imaging Spectrometer (ACIS)
- microchannel plate imager: High Resolution Camera (HRC)
- star tracker
- particle detector: Electron Proton Helium Instrument (EPHIN)
Some Major Discoveries of the Chandra X-ray Observatory
- the bulk of the X-ray background is made up of quasars, and almost all the rest is made up of faint galaxies;
- quasars repeatedly blow giant bubbles in the hot gas of clusters of galaxies, heating the gas and preventing it from condensing onto the quasar, so shutting off the quasar in a thermostat-like 'feedback';
- tenatively, the space between the galaxies in the nearby universe is filled with hot tenuous gas which, when added up, contains more matter than all the stars and galaxies;
- pulsars are surrounded by winds of magnetized gas moving close to the speed of light;
- an unknown region around the black hole at the center of our Milky Way galaxy emits strong bursts of X-rays every day;
- comets glow in X-rays because of bombardment by the solar wind.
- Many more examples are given on the Chandra Website.
External Links
- Chandra Public Website (Harvard-Smithsonian Center for Astrophysics)
- Chandra Mission Overview (Harvard-Smithsonian Center for Astrophysics)
- Chandra Images (Photo Album) (Harvard-Smithsonian Center for Astrophysics)
- Chandra Resources (Harvard-Smithsonian Center for Astrophysics)
- Where is the Chandra X-Ray Observatory? (Harvard-Smithsonian Center for Astrophysics)
Preview Image
Artists concept of NASA's Chandra X-ray Observatory. "NASA's Chandra X-ray Observatory Marks Seven Years of Stunning Revelations." (Source: NASA. Credit: CXC/NGST.)
Citation
Elvis, Martin (Contributing Author); Bernard Haisch (Topic Editor). 2008. "Chandra X-ray Observatory." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published April 15, 2008].
<http://www.cosmosportal.org/articles/view/135479/>
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