By most estimates, the neutron star, or pulsar, known as PSR1829-10 may not be much to look at. In fact, it cannot be seen at all. Scientists say that the star, located near the centre of the Milky Way, is a dense, dark orb. It is about 30,000 light years from Earth (light travels through space at 5.878 trillion miles per year) and was formed by a supernova explosion, the spectacular celestial event that occurs when the molten core of a star implodes, sending shock waves right through the universe. The pulsar, which emits radio waves at regular intervals, was one of 40 such stars discovered in 1985 by scientists at the Nuffield Radio Astronomy Laboratories at Jodrell Bank, 30 km south of Manchester, in northern England. Astronomers using Nuffield’s giant radio telescope found that sound pulses emitted by 39 of the neutron stars were unwavering. But the fluctuating responses from the 40th pulsar led them to a startling conclusion. In a letter published last week by the British journal Nature, they speculated that the 40th pulsar was being pulled out of its orbit by an orbiting planet. If that explanation survives the critical scrutiny of the scientific community, the planet will be the first to be detected outside of Earth’s Solar System.
Scientists have long predicted that other planetary systems must exist and would eventually be found somewhere in the universe. But despite some claims in the past, scientists have never been able to provide conclusive evidence to justify that theory. They said that the apparent discovery of another planetary system would have important implications for astronomers’ understanding of the universe, and could point the way towards the discovery of other planetary systems.
Said Paul Delaney, a professor of astronomy at Toronto’s York University: “Until now, we only knew for sure about one planetary system around ^ one star—the Sun. This z changes everything.” >
The evidence indicat5
ing that PSR1829-10 probably has at least one orbiting planet was assembled by three Jodrell Bank astronomers, Andrew Lyne, Matthew Bailes and Setnam Shemar. Lyne told Maclean ’s that after the observatory identified the new pulsars she years ago, the lab monitored each of the neutron stars on a regular basis using its 250-foot-diameter Lovell telescope that receives radio waves. Neutron stars cannot be seen with an optical telescope because their light cannot travel far from the galactic centre. But he said that he and his colleagues had noticed during routine observations with the giant telescope that ^ PSR1829-10 emitted an irregular g pattern of pulses. Lyne said that ^ after they detected that pattern, he ^ and Bailes, an Australian who began g working at the Nuffield Laboratories § only 18 months ago, tested their | observations against established “ mathematical models in an attempt to explain the fluctuations. Lyne said that it was not until last May that it occurred to them that they might have discovered a planet. Said Lyne: “It
was a purely serendipitous discovery.” The Jodrell Bank astronomers said that although the pulsar usually gave off a regular pattern of pulses, they observed that at times
the pulses would slow by one one-hundredth of a second. Then, three months later, the pulses would speed up again. After recording several cycles, Lyne said, the astronomers concluded that the pulsar was “being tugged a bit” by a planet with an almost circular, six-month orbit. “The most natural interpretation of this pulse variation is that the star has a companion orbiting around it,” Lyne said.
The discovery of another planetary system, which has yet to be confirmed by other astronomers, came after years of fruitless effort by astronomers around the world. During the past decade, scientists have been able to look ever deeper into space with the aid of sophisticated new telescopes capable of producing highresolution images of celestial bodies. Still, Delaney said that while these tools have come tantalizingly close to finding other planetary systems, none has provided enough evidence to satisfy the scientific community. He said that the powerful telescopes could not overcome the blinding glare that obscures the view of objects surrounding bright, relatively young stars, including the Sun. Because the Jodrell Bank telescope responds to radio waves coming from distant objects in space, rather than light, glare does not affect it.
Excitement among scientists over the possible detection of another planetary system was tempered by disappointment that it is too far away to be seen—and by the fact that the planet is unlikely to support any form of life.
Lyne said that the planet orbiting the pulsar probably has a mass of about 12 times that of Earth, and a circumference that may be two to three times that of Earth. The suspected planet apparently orbits its pulsar sun at a distance of about 67.24 million miles, roughly equal to the distance between the Sun and the planet Venus. Astronomers also speculated that the planet is under constant bombardment by high levels of deadly radiation from its host neutron star. Said Gerald Quinlan, a research associate at the Toronto-based Canadian Institute for Theoretical Astrophysics: “It is highly unlikely that any life form could survive in that environment.”
Although other scientists will almost certainly challenge the Nuffield team’s report to see if the interpretation bears scrutiny, some astronomers said that the evidence provided by Bailes, Lyne and Shemar appears convincing. “It is the strongest piece of substantive evidence that our Solar System is not unique,” Delaney said. For his part, Gordon Walker, a professor of astronomy at the University of British Columbia, said that the use of a radio telescope in the Nuffield experiments was similar to being caught speeding by a policeman’s radar gun. “It is very hard to argue with him when that number appears on the screen,” Walker said. Still, Lyne said that it was too early to regard his team’s findings as conclusive. “I think that the observations are secure,” he said. “But there may just be some-
thing else going on with that pulsar.”
If the Nuffield results are verified, the discovery will confront astronomers with new questions. Walker said that the presence of the planet next to a pulsar challenges the commonly held belief that a star’s planetary system would be wiped out by the catastrophic explosion of a supernova, which creates a pulsar. And even if it did survive, many astronomers say that the explosion should have knocked the planet out of its almost perfectly circular orbit. But Walker said that it was possible that the planet could have been formed by the debris from the host star’s supernova, which occurred about one million years ago. Said Walker: “That is not much time to allow a planet to form out of the debris.”
As scientists studied the Nuffield findings, Lyne, Shemar and Bailes said that they planned to do new experiments. Lyne said that there is some evidence suggesting that PSR1829-10 may have more than one planet. But he added that it could take up to 10 years to determine whether there are other planets. “It’s an exciting concept that our Solar System is not unique,” he said. “It gives us another step forward in projecting our imaginations into outer space.” Clearly, if the theory advanced by Lyne and his colleagues is correct, many more astronomical horizons remain to be crossed.
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