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Radio astronomers are willing to advance such gaudy theories, but only as conjecture. They cannot be sure about anything; the sky is too full of mysteries that they cannot begin to explain. A strong radio source that has been labeled M87, now proves to be a galaxy that can be photographed in visible light. It has a strange jet of glowing material that extends from one side and reaches many thousand light-years beyond its normal circumference. Does this jet have something to do with the galaxy's radio waves? It probably does, say the radio astronomers, but they do not know why.
Another exciting mystery results from the recent discovery that magnetic fields are common in space, perhaps even in the empty reaches between the galaxies. Radio waves reveal the fields and measure their strength, but no one knows the origin of this mysterious force. Apparently it is an important feature of the universe, and may affect its behavior in many different ways.
Loud Stars. Most true stars in the Milky Way galaxy maintain fair radio silence, but a few of them transmit powerful radio waves that have the astronomers baffled. About half a dozen radio stars have been identified optically, and they prove to emit peculiar assortments of visible light. Astrophysicists are busily studying these spectra, hoping to find some connection between them and the stars' radio loudness.
Radio astronomers are particularly intrigued by the special waves given off by cold hydrogen floating between the stars. These waves are a little longer than 21 cm. long when they leave the hydrogen cloud where they are generated. If they are slightly shorter than that when they are measured by an earthly radio telescope, this means that the hydrogen cloud must be moving rapidly toward the earth. If the waves are longer, the cloud is moving away. So the 21-cm. waves provide a handy tool for measuring the speed of the hydrogen clouds that form an important part of the Milky Way galaxy. Some of the clouds are moving close to the galactic nucleus, which looks in optical telescopes like a close-packed, featureless mass of glowing stars. But the 21-cm. waves reach deep into this stellar fog. They report that vast streams of hydrogen are flowing out of the nucleus, and none are streaming back. Where does the hydrogen come from? One theory holds that it collects from the thin halo that surrounds the galaxy. Another suggests that it is transformed out of some unobserved and heretofore unimagined state of matter.
Life in the Universe. The bold radio astronomers are ready to tackle anything, even the ancient problem of alien life in the universe. Most astronomers agree that the Milky Way galaxy has millions of stars with planets capable of supporting earth-style life. Few if any of them believe that human space voyagers can ever cover the enormous distances that separate the stars. But radio waves cover that range already, and perhaps some not-too-distant stellar system, which includes a planet that has developed a high civilization, is even now sending radio messages in the hope that someone will hear them. Radio astronomers at Green Bank have done a little listening for such messages. They have heard nothing meaningful, but they hope to try again.