Sky & Telescope January 1983 [antikvár]

The X-ray Dets of Centaurus A and M87Eric D. Feigelson, Massachusetts Institute of Technology, and Ethan J. Schreier, Space Telescope Science InstituteH. Arp used the Hale 5-metcr telescope under ideal conditions to record this image of the peculiar galaxy M87 and its famous jet.Among the great number of galaxies . seeti in the sky, a small fraction perhaps one percent stand out because of unusual and intense emission. Most galaxies radiate primarily in the visible region of the spectrum since they consist of stars which, like the Sun. have surface temperatures of a few thousand degrees Kelvin. Such normal systems, including our Milky Way. typically emit a million times more energy at optical wavelengths than in X-ray or radio bands. But some galaxies are sources of infrared, optical, X-ray, and even, in some cases, gamma radiation too powerful to be produced by their constituent stars.This type of nonstellar emission usually emerges from a highly luminous, compact region at the center (nucleus) of the galaxy; it generates as much as 1,000 times more energy than all of the galaxy's stars combined. This characteristic, together with variability on time scales as short as hours, requires that the radiation be pro-