Fantastic Signals from Space

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.

After remaining silent about the discovery for seven months, the Cambridge team published its findings and tentative conclusions in Nature, setting off a flurry of activity among U.S. scientists. Focusing Cornell University's giant radio telescope near Arecibo, Puerto Rico, on the one pulsar whose position was given by the British, Astronomer Frank Drake confirmed the rapid, regular signal and discovered that it was ten times as powerful at 111 MH (for megahertz: 1,000,000 cycles per second) than at any other frequency. "This has been the biggest bombshell that I can remember in radio astronomy," he says. Caltech Astronomer Maarten Schmidt, who discovered the strange nature of quasars, calls the finding "fantastic, incredible."

Oftentimes Overdone. U.S. scientists have already devised a host of theories about pulsars. Yeshiva University Astrophysicist A.G.W. Cameron and Caltech Astronomer John B. Oke believe the mysterious objects may be white dwarfs, Cameron suggesting that their frequency of oscillation is actually a harmonic of the lower frequency assigned to dwarfs by current theory. U.S. Naval Research Physicist Herbert Friedman of the U.S. Naval Research Lab oratory and Cornell Astronomer Thomas Gold support the neutron-star hypothesis. Gold speculates that the first pulsar identified may be an extremely dense body as small as six to 60 miles in diameter that rotates once every 1.337 seconds.

Jodrell Bank Astronomer Bernard Lovell suggests that the observed pulsations "must involve a large fraction of the total energy available in a star like the sun." Thus, he says, "any intelligent beings who were ever in the neighborhood of such events would have been extinguished long ago." But some astronomers feel that they must investigate pulsars more closely before absolutely ruling out the possibility that they are creations of an intelligent race.

"Oftentimes this intelligent-civilization bit has been overdone," says Astronomer Schmidt, "but if you want to attribute anything to a civilization, then this is the best case we have had so far." The chance that pulsar signals do come from an intelligent race, agrees Arecibo's Drake, "does remain a possibility." At week's end, Cambridge astronomers reported in a second Nature article that a faint blue star had been tentatively identified as one of the pulsars, providing still another clue that may eventually help solve astronomy's latest and most exciting enigma.

*Incredibly dense bodies of tightly packed neutrons only ten miles in diameter that are supposedly remnants of supernovae.

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