first image of Puppis A
Credit: S. Rappaport et al. (1979, ApJ Letters, 228, 99); S. Snowden

Origin of X-ray Astronomical Photography

Images of the X-ray emission from astronomical objects are hard to make, since x-rays are difficult to bring to a focus. This is because incident X-rays either pass right through or are completely absorbed by most materials. In the early 1950s it was realized by Hans Wolter that X-rays could be focussed by a system of mirrors if the X-rays scattered off the mirror surface at grazing incidence (much like a stone can skip off the surface of a lake). The so-called "Wolter type I" X-ray mirror configuration, in which x-rays are focussed by sets of parabolic and hyperbolic mirrors arranged in concentric shells, has become the most common type of X-ray mirror configuration used in astronomy. This configuration was first used to obtain an X-ray photograph of an astronomical object (outside the solar system) by a group from MIT lead by Saul Rappaport. Their image of the Puppis A supernova remnant is shown above left, while a ROSAT HRI observation of Puppis A is shown for comparison on the right. Though crude by today's standards, this image clearly showed the complex nature of the X-ray emitting regions in this and other supernova remnants and helped pave the way for later breakthroughs by the EINSTEIN and ROSAT telescopes, and the exquisite images obtained today by Chandra and XMM-Newton.

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Page Author: Dr. Michael F. Corcoran
Last modified May 27, 2001