(2 of 10)
A significant step toward this discovery occurred in 1931 when Radio Engineer Karl Jansky of the Bell Tek phone Laboratories accidentally found that radio signals were coming from outer space. But astronomers were slow to recognize that such radio energy—the only radiation besides visible light that can penetrate the earth's atmosphere over a wide frequency range—might offer a powerful new tool for exploring the universe. Little was done to take advantage of the new tool until wartime radar research provided accurate directional antennas and improved electronic techniques.
Immediately after World War II, astronomers all over the world hastened to build steel-ribbed parabolic dishes and ungainly rows of spindly antenna arrays. They even lined a small valley with wire mesh and began to scan the skies for radio sources. These pioneer radio astronomers scanning the sky "saw" only blotchy, vague shapes—like street lights dimly seen through the fog.
To sharpen their vision, they began building larger antennas. In 1946, they devised a new technique: radio interferometry, in which two antennas located at a considerable distance from each other are tuned to radio signals from a single source. Because the radio waves arrive at the antennas at slightly different times, they interfere with each other in a pattern that more sharply defines the position of the source.
Gradually, as the accuracy of radio telescopes improved, the vague shapes in the sky contracted until it became possible for radio observers to direct optical astronomers to smaller and more manageable areas. In 1949, astronomers using these directions spotted the first visible object outside the solar system that was associated with a discrete radio source: the Crab Nebula, the remnant of a star explosion (or supernova) in the earth's Milky Way galaxy. Shortly afterward, they identified the first visible source outside the Milky Way: a large galaxy 50 million lightyears* from earth. In the next decade, as radio and optical astronomy continued their fruitful alliance, about 100 additional galaxies and supernovas were recognized as powerful radio transmitters.
Intimate Secrets. Mystery remained. When optical astronomers turned their huge glass eyes on some of the areas of sky manned by radio astronomers as sources of powerful emissions, they found only assortments of faint, nondescript stars. Then, in 1960, aided by pinpoint data supplied by Cambridge University's radio astronomers, and Caltech's Owens Valley Observatory, Caltech astronomers discovered that one stream of powerful signals was coming from what appeared to be a small, faint star. During the next few years, as radio telescopes continued to supply increasingly precise data, the California astronomers discovered three more faint, mysterious objects. Though they were undistinguished in appearance, they stood out like powerful beacons in the radio sky. For want of a more descriptive term, the objects came to be called "quasi-stellar sources," a name that was quickly contracted to "quasars," and reluctantly adopted by astronomers.