Pulsar That Excited Astronomers Was ‘All a Mistake’
An extremely unusual pulsar discovered a year ago in the remnants of a new supernova was actually only a spurious electronic signal from a television camera located on Earth, researchers confirmed Monday.
The pulsar, an extremely dense mass of subatomic particles called neutrons, startled the astronomy community when it was discovered by a team from Caltech, the Lawrence Berkeley Laboratory and the Los Alamos National Laboratory because it appeared only briefly and seemed to be spinning so fast that it should have been ripped apart by its own angular momentum.
The apparent discovery spurred researchers to develop a broad variety of new theories to explain its existence, said astronomer Kenneth Brecher of Boston University, sparking many scientific papers that have been published or are now in press.
But astronomer John Middleditch of the Los Alamos National Laboratory in New Mexico brought the excitement to a halt--at least temporarily--and rendered those scientific papers meaningless last week when he notified other researchers of the error. Late Sunday, he also withdrew a paper scheduled for presentation at a meeting of the American Assn. for the Advancement of Science here, saying that, “It was all a mistake.”
The mistake does not mean there is not a pulsar at the middle of Supernova 1987A, which exploded onto the astronomical scene in 1987. In fact, most scientists believe, and conventional theory predicts, that there is one buried beneath all the debris associated with the stellar explosion that created the supernova. It simply hasn’t been seen yet.
Only 160,000 light years distant, it is the closest and hence the brightest supernova observed since the invention of the telescope. Its discovery triggered a massive gathering of data and promised to reveal significant new insights into astronomical processes.
In January, 1989, Middleditch and his colleagues went to the Cerro Tololo Inter-American Observatory in Chile with an exceptionally sensitive new light detector to look for the pulsar that was assumed to have been formed in the supernova. Pulsars, which can contain the mass of the sun in a body no more than 10 miles across, rotate extremely rapidly, emitting pulses of light like the beacon of a lighthouse at regular intervals of small fractions of a second.
As soon as they turned on the detector, “a signal that looked like a pulsar came blasting through,” Middleditch said Monday. “The data looked really good; it had features in it really indicative of a pulsar.” But the object seemed to be rotating exceptionally rapidly, 1,968 times per second. At that speed, it should have flown apart almost instantly, and theorists were hard pressed to develop explanations for its existence.
Other researchers were unable to detect the pulsar, and when Middleditch and his colleagues looked again in July, they couldn’t find it either. Most people assumed it was obscured by dust from the supernova.
Two weeks ago, however, team members went back to Cerro Tololo with an even more sensitive detector. They observed the pulsar again. But when they pointed the four-meter telescope at the Crab Nebula, which does not have a pulsar, “the pulsar signal came blasting through again,” Middleditch said.
Further examination revealed that the signal was coming either from a television camera on the telescope that is used to orient it, or from an interaction between the camera and the sensitive detectors. Without realizing it, Middleditch’s team had switched to a different camera after the initial pulsar observation, and it was not until they happened to use the first camera again that they discovered the problem.
The team immediately withdrew a paper that was pending in the journal Science and began notifying other researchers, who were “pretty disgusted,” Middleditch said. “I was pretty disgusted myself.”
But the erroneous discovery will have many benefits anyway, he said. It has accelerated an upgrading of the facilities at Cerro Tololo, which eventually may lead to a genuine discovery of the pulsar.
Meanwhile, he said, “It’s better to have observed and issued a false report than never to have observed at all.”
Astronomer Richard Muller said the team found a supernova in another galaxy only a couple of days after discovering their error. “That really buoyed us,” he said. “We felt it was God paying us back for the practical joke he had played on us.”
