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Living Universe. A list of the radio sights visible through these varied telescopes would fill an enormous book, but radio astronomy is developing so fast that no such book is likely to be written for years. Still, the radio window has already brought the universe to life in numberless unexpected ways. Even the moon, just about the deadest object in the solar system, sends out radio waves that tell something about its temperature and about the material on its surface.
The planets have come to life too. Venus sends waves which hint that the temperature under its clouds is much too high for earth-type life. Jupiter pulsates with many kinds of radio waves. One kind comes from an easily observable shell
around the planet, is apparently generated by a powerful radiation belt similar to the Van Allen radiation belt that surrounds the earth. Other Jovian radio waves seem to be generated by gigantic thunderstorms.
But the planets are not the main concern of radio astronomers, who tend to think of them merely as distant parade grounds for space cadets. Even the sun, which sends out rich chords of radio waves, is not a chief attraction. The astronomers' keenest interest is focused on much more distant space, from which the waves bring news of strange occurrences. The third strongest single source in the sky is a famous astronomical object, the Crab Nebula, the turbulent, gaseous wreck of a star that turned into a supernova and blew itself to shreds on July 11, 1054 A.D.—an event that was duly recorded by Chinese astronomers. After 908 years, the Crab's gases are still churning violently, and as the electrons that they contain move through magnetic fields, they still send out a vast amount of radio energy.
Radio Galaxy. The strongest "radio star" in the sky had the astronomers baffled for many years. Its powerful waves came from a patch of sky in the constellation Cygnus, and optical astronomers could find nothing there. At last the Palomar telescope, guided by a new and extremely accurate radio fix, photographed an extraordinary scene that looked like a collision of two enormous galaxies 500 million light-years away. Galaxy collisions are possible, though unlikely, and they might emit radio waves because of churning gases between their hundreds of billions of stars.
But most radio astronomers no longer think that such a collision can properly explain the stupendous radio energy that streams out of Cygnus A. For one thing, the energy does not come from the central part that is optically visible. Strangely, it comes from two 'spots on opposite sides of the center. The sky is full of these double radio sources. One theory holds that they are galaxies that have exploded. Electrons released in the explosions may have been steered by magnetism and finally gathered at spots far away from the central wreckage. A vast catastrophe of this sort might well be a normal stage in the long life of a galaxy. Perhaps man's own Milky Way galaxy will end in this manner, its stars popping like firecrackers and its death cry sounding in radio waves across the universe.