CygnusA

In 1953 the galaxy associated with Cygnus A, the second brightest radio source outside our solar system was identified. (The sun is the brightest radio source in the sky and the Cassiopeia A radio source the brightest outside the solar system.) The Very Large Array radiograph of Cyg A was shown in Figure 1.4 and it reveals magnificent detail. The radio lobes manifest as beautiful diaphanous filaments whose subtle patterns belie the amazing energies associated with this source. A

faint yet stunning radio jet. less than a tenth of a percent as bright as the lobes, can be seen heading toward the northern lobe. The radio double is centered on a peculiar galaxy, which was originally believed to be galaxies in collision. In the 1950s two famous astronomers, Walter Baade and Rudolph Minkowski, argued about this, and bet a bottle of whisky or a thousand dollars, depending on whose version of the story you believe, on whether or not Cygnus A was a colliding galaxy. The issue was settled—against the colliding galaxy hypothesis—when it was realized that double radio sources were too common to be explained by intergalactic collisions. However, since then the explanation is again in question, because galactic cannibalism resulting from close encounters between galaxies in near collision within one another may be at work in many, if not all, radio galaxies. We must allow that Baade and Minkowski should both have won.

Several "hot spots" can be seen in the radio lobes in Figure 1.4. These are characteristic of many double radio sources and are often found at the end of the axes of the jets, where material crashes up against the boundary separating the radio lobe from intergalactic matter.

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