Taking the Pulse of Pulsars

Under the careful scrutiny of increasing numbers of scientists around the world, astronomy's newest sensation--the pulsars--continued to beep away last week, confounding observers with the breathtaking regularity of their signals. With almost unseemly haste, astronomers and astrophysicists conjured up possible explanations for the new signals from space and rushed them to publications like Nature and Science, hoping to be first in print with the theory that eventually is proved correct. In London a crowded, excited meeting of the Royal Astronomical Society was devoted entirely to the pulsars.

Somewhat belatedly, Astronomer Anthony Hewish, leader of the Cambridge University group that discovered pulsars (TIME, March 15), revealed the positions and the pulse rates of pulsars 2, 3 and 4. One of them blips every 1.27 seconds, another at 1.19-second intervals--close to the 1.34-second period previously reported for pulsar 1. Pulsar 4 pulses significantly faster: every quarter of a second. In addition, Hewish estimated that the fast-pulsing source is only 50 light-years away, compared with the 200-light-year distance he calculated for pulsar 1.

Blue Star. Using the coordinates given by Hewish, Astronomer Frank Drake trained the giant Arecibo, Puerto Rico, radio telescope on pulsar 3 and discovered that each of its signals was composed of two closely spaced peaks. The peaks were so sharp, he said, that the signal may originate from an object as small as a few hundred miles across; if pulsar 3 were much larger, the peaks would be gradual and less distinct. Using England's Jodrell Bank radio telescope, Astronomer Graham Smith discovered that the radio waves from pulsars are polarized, indicating that they pass through a magnetic field on their way to the earth.

Checking on the faint blue star that Cambridge University astronomers have associated with pulsar 1, Astronomer William Liller located it on a number of Harvard Observatory photographs taken between 1897 and 1952. During that interval, he reported, the average visible light from the star had not varied significantly. And in California, Astronomer Allan Sandage announced that he plans to train the 200-in. Mount Palomar telescope on the blue star to detect any second-by-second variation in its light intensity that might coincide with pulsar 1's radio variation.

Meanwhile, pulsar theories continued to proliferate beyond the pulsating neutron-star and white-dwarf-star theories first suggested by Cambridge astronomers. Princeton Astrophysicist Jeremiah Ostriker suggested that the signals might be caused by rapidly rotating white dwarfs with a local disturbance on their surfaces. Signals from the disturbance would sweep across the earth like a lighthouse beacon once during each rotation of such a star. British Astrophysicists Fred Hoyle and J. Narlikar propose that the signals are connected with supernovas, or exploding stars.

Enormously Wasteful. Several scientists have theorized that the pulses may be caused by white dwarf or neutron stars rotating rapidly around each other in a binary system; any particles passing through the rotating and intense magnetic field that must exist between the two stars would produce strong radiation that would periodically sweep the earth. Others have suggested that the intense gravity of a star in such a binary system would act as a lens, periodically intensifying and focusing the radiation from the twin star passing behind it.

There still is the remote chance, some astronomers feel, that the signals are being sent by distant, advanced civilizations. While admitting this possibility, Astronomer Drake, for one, stresses that there are strong arguments against it. The signals, he notes, are transmitted over a very wide range of frequencies--an "enormously wasteful" procedure not to be expected of superintelligent beings. And if the signals from pulsar 1 are being transmitted in all directions from a distance of a few hundred light-years away from earth, the power level of the transmitting source must be about ten billion times greater than the entire electrical generating capacity of our civilization--"too high," Drake says, "to be plausible."

Most scientists agree with Drake's reasoning, and a slight majority now appears to favor the theory of extraordinary, vibrating white dwarf stars as the probable source of the signals from space. Said Jodrell Bank Astronomer Smith at the close of the Royal Astronomical Society meeting: "It looks as if the little green men are now white dwarfs."

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