For a few electrifying days late last month, a spectacular rumor spread among U.S. scientists. British astronomers had detected signals so regular and pulsating so rapidly from four different regions in outer space that they might have been sent by intelligent beings. Last week, when details of the British findings reached the U.S., the possibility that the pulsations had been artificially produced by an advanced civilization seemed remote. But even if the causes were natural, scientists on both sides of the Atlantic were in firm agreement that discovery of the pulsing signals, named "pulsars" by the British, was one of the major astronomical finds of recent times—perhaps equal in importance to the discovery of the nature of quasars in 1963.
Pulsars were first detected last sum mer, shortly after Cambridge University's Mullard Radio Astronomy Observatory began using a new and highly sensitive radio telescope. Investigating the angular size of a quasar, a pigtailed, 24-year-old Irish graduate student named Jocelyn Bell noticed some strange, pulsating signals that were "so weak they were hard to pinpoint." Working in excited-secrecy, a Mullard Observatory team led by Astronomer Anthony Hewish began an intensive analysis of the pulsations.
Breathtaking Regularity. Getting a good fix on one of the signals, the astronomers calculated that it came from an object no more than 4,000 miles in diameter—about half the size of the earth—that was no more than a neighborly 200 light-years away. The signals occurred with breathtaking regularity, one every 1.337 seconds. "Our first thought," says Radio Astronomer Martin Ryle, director of the Mullard Observatory, "was that this was another intelligence trying to contact us."
The possibility was so intriguing to the British astronomers that they began referring—only half jokingly—to their strange radio sources as "LGMs" (little green men). But two factors eventually persuaded them that the signals were not artificial: the location of three ad ditional rapidly pulsating sources after discovery of the first, and the lack of any evidence that the signals were being transmitted from a planet.
"Multiplicity suggests a natural phenomenon," says Astronomer Hewish. "It would be stretching the imagination too far for all of them to be generated by intelligent beings." The Mullard team searched in vain for slight changes in signal frequency that would indicate it came from a planet or a double star system; in orbit around a star, for example, a planetary transmitter would alternately approach and recede from the earth, producing a Doppler effect that would first increase and then decrease the frequency of its signal.
Gravitational Collapse. Weighing the possibilities, the Cambridge astronomers decided that the signals might be the natural oscillations of dying stars that had shrunk by gravitational contraction into white dwarfs—or into neutron stars,* which have been postulated but never actually discovered. But this explanation has its difficulties: if they do oscillate, according to theory, white dwarfs should pulse once every eight seconds or slower, neutron stars every thousandth of a second.