Newborn Pulsar’s Discovery Puts New Spin on Theories

Astronomers have detected a newborn pulsar, a superdense star that is spinning about six times faster than any previously observed pulsar and faster than scientists had thought possible.

The new star was found last month in the center of a supernova 10 million light years away that exploded two years ago. It marks the first time that researchers have observed a pulsar--so named because it emits pulses of radiation--so soon after its birth, giving them a “once-in-a-lifetime” chance to observe this stage in the evolution of stars.

“By detecting and observing it so early in its cycle, we may be able to learn not only how pulsars are born, but also about the structure of . . . the cloud of heavy elements that is thrown out of the core during the supernova explosion,” astrophysicist Carl Pennypacker of the Lawrence Berkeley Laboratory, one of the pulsar’s discoverers, said Thursday.

“I think the discovery is a terrific thing,” said astronomer Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. “Everybody suspected it would be found, but there is a big difference between that and actually seeing it.”

But if scientists expected to see the new pulsar, they were not prepared for its unusual properties as described by Pennypacker and his colleagues.

The pulsar, which has the mass of the sun concentrated into a ball about 14 miles in diameter, is rotating at a speed of 2,000 revolutions per minute.

“I’m astonished, simply astonished,” that it could rotate at that rate, said astronomer Joseph H. Taylor of Princeton University in New Jersey.

Taylor noted that the pulsar’s speed is about twice as fast as the maximum theoretical rate at which a pulsar could spin without blowing apart.

According to most theories, a pulsar is the next-to-last phase in the life cycle of stars, with a mass at least eight times as great as the sun’s.

During its lifetime, a star burns through all the lighter elements of the periodic table, forming heavy elements out of light elements like hydrogen (as the sun is doing now), and eventually consuming the heavier elements themselves. The process stops with the production of iron, and the star explodes, becoming a supernova.

What remains at the core is a pulsar, a dense, spinning object composed entirely of neutrons--uncharged elementary particles--with an unimaginably strong magnetic field, about 1 trillion times as strong as the Earth’s. These fields produce searchlight-like beams of radiation that are seen as a pulse when the neutron star’s spin sweeps them past the Earth.

Scientists have been intensively monitoring the supernova, which is only visible in the Southern Hemisphere, since it first flared into view on Feb. 23, 1987, the first supernova that had been observed since the telescope was invented 350 years ago.

They have subsequently observed most of the physical characteristics that theoreticians had predicted for a newborn supernova. The discovery of the pulsar, said Kirshner, “is the last piece of the puzzle falling into place.”

Pennypacker and his colleagues also reported that the frequency of the light emitted by the pulsar is varying in a regular pattern, suggesting perhaps that the pulsar is a double system with a smaller object rotating around a twin.

“That is a surprising conclusion,” said astrophysicist Roger Blandford of Caltech. “If their measurements are correct, we have two substantial puzzles there”--the variability and the high speed of rotation.

The multinational team of observers who discovered the pulsar used specially produced light sensors fitted onto the Cerro Tololo Inter-American Observatory in Chile. They found it while processing data from seven hours of observations made on the night of Jan. 18. Subsequent observations later in the month, failed to show the pulsar, but that could be caused by debris from the supernova or some variability in light emission.