Findings May Alter Theories of Universe : Astronomy: Researchers have discovered planets orbiting a pulsar, and mysterious bursts of powerful radiation from unknown sources. Other studies back a key part of Einstein’s Theory of Relativity.

Scientists say they have discovered two and possibly three planets orbiting a distant star, suggesting that other planetary systems can form under the most unfavorable conditions and probably are common throughout the universe.

The discovery was presented today as part of a smorgasbord of astronomical discoveries that could rewrite a number of theories about the universe.

In a series of research papers in today’s issue of the British science journal Nature, scientists also reveal that they have discovered mysterious bursts of powerful radiation from unknown objects that appear to be scattered around the universe.

Both of those discoveries pose more questions than answers, but there was good news for some astronomers who may be longing for stability in their field: Other new research strongly supports a key part of Albert Einstein’s Theory of Relativity.

The various findings, if confirmed, could force revision of some theories about the universe.

For decades, scientists have searched for evidence of other planets around other stars, because the more planets there are, the greater the chances are of extraterrestrial life. So far, the only way to discover planets is to infer their existence from the behavior of their host star, because any star is so bright compared to its planets that the smaller bodies cannot be seen with optical telescopes.

Most stars with planets would appear to wobble when observed for long periods because the star and its planets would revolve around their common center of mass. So, in recent years, astronomers have sought stars that change position slightly, because orbiting planets would be the most likely explanation for such a change.

Several potential planetary systems have been identified lately, but the most compelling evidence is perplexing because it suggests that planets have formed around very dense, spinning stars called pulsars. Few experts expected planets to be found around pulsars, because those stars are believed to be formed in the violent explosion of a previous star that should have swept away any dust and particles that could have coalesced into planets.

Last year, British astronomers reported evidence of a single planet around a pulsar, known only by a number, PSR12829-10, but many scientists doubted that finding because no one had expected pulsars to have planets.

But American scientists have come up with evidence that supports the British finding, and they take it a step further: They say they have discovered two, possibly three, planets orbiting another pulsar, PSR1257+12.

The discovery suggests that the formation of planets “can take place under surprisingly diverse conditions,” said Alexander Wolszczan of Cornell University. Wolszczan is also a resident astronomer at the Arecibo Observatory in Puerto Rico, site of the world’s largest radio telescope, where he did much of the work. Joining him was Dale A. Frail, who measured the pulsar’s position with the Very Large Array, a series of radio telescopes in the New Mexico desert.

The pulsar is about 1,300 light-years from Earth and is so faint that it can barely be seen by even the largest telescopes. It spins at an astonishing 162 times a second, and as it turns it sends out a radio beacon that sweeps the skies like a spinning lighthouse. As the beacon sweeps past the Earth, it is received as a pulse--thus the name pulsar--and it arrives with such precision that it could actually be used as a very accurate clock.

But when the two scientists examined the star, aided by Cornell University’s National Supercomputer Facility, they discovered that the pulses were not quite as precise as they should have been. Sometimes they arrived a little late, and sometimes a little early.

By computing the variation in time, they determined that the changes were caused by a slight movement of the pulsar, leading them to conclude that it was first being pulled farther away and then closer to the Earth by at least two planets. Further analysis suggested that the planets were about the same distance from the pulsar as Mercury is from the sun, and with a mass about three to four times greater than the Earth’s.

Another slight variation suggests that a third planet, a little farther from the pulsar than the Earth is from the sun, may also be orbiting the star.

The discovery reveals the precision of modern instruments in that the scientists were able to measure the pulsar’s movement of only about 550 miles from a distance of 7,500,000,000,000,000 miles away.

Wolszczan said the pulsar was once part of a binary system, meaning it had a companion star. About 1 billion years ago, the star with the greater mass exploded in a supernova, and the debris collapsed into a tiny pulsar that has a greater mass than the sun but is only about six miles in diameter. The violence of the explosion probably vaporized the companion star, he said, and while most of that debris was undoubtedly swept away by the blast, some was eventually pulled back by the pulsar’s powerful field of gravity.

Debris from the companion star would have formed a disc around the pulsar, causing it to spin faster and faster until it coalesced into planets, Wolszczan said.

If other scientists find similar evidence in this rapidly expanding search, it means that planets have formed around many stars and thus the chances of life existing elsewhere are enhanced.

But these planets probably have no life, Wolszczan said. Powerful bursts of radiation from the pulsar constantly sweep the planets, and that would almost certainly sweep away any atmosphere, probably leaving them as barren chunks of rock.

While some scientists look for planets, others have been searching for the source of mysterious bursts of gamma rays. These extremely energetic bursts have been studied since they were accidentally discovered in 1967 by a satellite designed to monitor nuclear test ban violations. The bursts were thought to be coming from near the center of the Milky Way Galaxy, and many scientists believed they were being produced by matter being stripped apart by a black hole.

It remained a mystery, because the center of the galaxy is so dusty that it cannot be penetrated by optical telescopes.

But the mystery has deepened considerably with the latest results from the “burst and transient source experiment” on the Compton Gamma-Ray Observatory, which was built by TRW Inc. of Redondo Beach.

When the observatory looked for gamma ray bursts, it found them, but they were coming from everywhere, not just from the center of the galaxy.

“Everybody had believed they were coming from the galaxy,” said Charles Meegan of NASA’s Marshall Space Flight Center in Huntsville, Ala. “The big shocker is, they are not (coming just from the galaxy.)”

Instead, the bursts appear to be randomly distributed across the sky. And if they were being produced by black holes gobbling up matter in the center of galaxies, they should be far more plentiful around other nearby galaxies. But they are not.

The scientists reported that they have found 153 bursts, and there is “no apparent clustering of bursts” around this galaxy or any other. They conclude that the bursts must be coming from objects either very close or very far away.

“Very close is a possibility,” Meegan said in a telephone interview, “but no one has come up with any reasonable suggestion for what the source could be.”

Or they could be very far away, but if they are on the fringes of the universe they would have to be so powerful that their presence should have been detected in many other ways.

“No one has come up with any reasonable suggestion for what it could be,” Meegan said. “It’s a complete mystery right now.”

Mysteries are nothing new to astronomers, especially since Einstein turned their world upside down with theories that seemed to challenge common sense. Einstein postulated that the geometry of space is curved, and everything, including gravity, is influenced by that curvature. A black hole, for example, is so dense with its gravity so intense that space folds in around it.

Proving Einstein’s theories has been one of the most formidable challenges in science, yet many aspects of his work have been confirmed. Scientists determined long ago that when light passes the sun, for example, it is bent in conformance with the curvature of space.

But what about more distant objects? Einstein theorized that two dense stars revolving around each other should send out gravity waves that would ripple across the curvature of space, like waves from a pebble tossed into a pond.

Joseph Taylor of Princeton University has been working on this problem for 10 years, and today he and several colleagues present evidence that supports Einstein’s theories.

Using the Arecibo Observatory, the scientists studied three pairs of binary systems, in which a pulsar and a neutron star are orbiting around each other. They measured the pulses from each of the pulsars precisely, and then computed the orbits.

If Einstein had been wrong, the orbits should have conformed exactly to paths worked out nearly three centuries earlier by Isaac Newton. If Einstein were right, however, space in the vicinity of the two dense objects should have been curved slightly, making the orbits a little irregular.

The scientists found the curvature.

“General relativity passes these new experimental tests with complete success,” they concluded.

Planets Discovered

Astronomers say they have discovered two and possibly three planets orbiting a distant pulsar. The evidence confirms a similar discovery last year, and it suggests that planetary systems may be common throughout the universe.

Creation of a Pulsar

A. Pulsars are formed when a red giant “progenitor” star exhausts its fuel and collapses.

B. The star explodes violently into a supernova, in which the core is compressed into a neutron star.

C. If the neutron star spins, it creates a powerful magnetic field that sweeps the heavens like a beacon from a lighthouse. When this occurs, the neutron star becomes a pulsar.

The Planets and the Pulsar

* A pulsar normally emits regular radio signals.

* But in this case, the gravitational influence of at least two planets is believed to be causing the pulsar to oscillate, or wobble.

* The pulsar’s wobbling is causing a variation in the time it takes the radio signals to reach the Earth, indicating the presence of planets.