Pulsar Discovery Makes Astronomers Start Over : Space: They must rethink their ideas on where the mysterious remnants of exploding stars reside.
In what has turned into a marathon lesson in humility, astronomers have discovered that something is terribly wrong with their understanding of pulsars, those mysterious radio beacons that were born during some of the universe’s most violent moments.
Until recently, astronomers thought they knew where to look for pulsars, which are remnants of exploding stars. But when they looked at an area of the sky where nobody expected to see them, they found thousands of pulsars, some spinning so fast that an observer standing on the surface would be traveling at nearly the speed of light, the American Astronomical Society was told here Wednesday.
The discovery means that astronomers, who are seeing some of their most cherished theories on the evolution of the universe challenged by new data, will now have to rethink their ideas on where pulsars reside.
The newly discovered pulsars were found in ancient, compact collections of stars known as globular clusters. Most experts had thought that the processes that create pulsars would also destroy these tightknit clusters.
Radio astronomer Shrinivas Kulkarni of Caltech, who announced the discovery, said five pulsars were found in one cluster, “and by no means is the game complete.”
Kulkarni said the discovery probably represents just “the tip of the iceberg.” He estimated that the globular clusters on the fringe of the Milky Way probably contain a total of 2,000 to 10,000 pulsars.
“This is an amazingly large number of pulsars,” he said.
The discovery was made with the Arecibo Radio Telescope in Puerto Rico. As a result of the finding, Kulkarni said, “we are confused about how these globular clusters began.”
Pulsars are rotating forms of neutron stars, which are the most dense objects in the universe. Pulsars are formed when a star as massive as the sun exhausts its fuel and explodes. According to the theory, the resulting debris then collapses into an extremely dense object, a neutron star. If a companion star was orbiting nearby, the neutron star would spin because of the influence of its companion. And if the neutron star had a magnetic field, it would become a pulsar. A powerful radio signal from the pulsar would sweep the heavens, and if it passed over the Earth, the pulsar would appear to blink on and off like a radio beacon. In the case of rapidly spinning pulsars, the beam would turn on and off many times each second.
Several scientists said they had not expected to see pulsars in globular clusters because the stars there are the oldest in the galaxy and older stars were thought to be too small to collapse into neutron stars. Also, the violent stellar explosions should have swept out stars in the tightly formed clusters, thus changing their composition dramatically.
“Neutron stars are destructive to their own environment,” Kulkarni said. “The formation of a globular cluster must have been something very special.”
He said the evidence indicates that all of the pulsars were created “after the cluster was formed and all at the same time.”
The discovery will keep theorists busy for a while, and it was only one of several major discoveries announced here Wednesday.
For the first time, data from the troubled Hubble Space Telescope also played a key role in a number of findings. The orbiting telescope was launched with a flawed primary mirror, thus severely reducing the research that can be done with it, but scientists announced, gleefully, that their efforts to use the telescope to carry out research that cannot be done from the ground had met with some success.
“The impact on image quality (from the mirror flaw) is very large,” said James Westphal of Caltech, principal investigator on the Hubble’s Wide Field/Planetary Camera. But he added that technicians on the ground had been able to “do wonderful things” to improve the images through computer enhancement.
He admitted that some results “are not anything like we had hoped,” but he added that some images are “full of wondrous, gorgeous and fascinating things, most of which we don’t understand.”
For example, Nino Panagia, a scientist with the Space Telescope Science Institute, said the resolution was clear enough for the European-built Faint Object Camera to pinpoint the distance to a star that exploded in 1987. The star, called Supernova 1987A, is exactly 169,000 light years from Earth, Panagia said. Previously, the supernova, located in a nearby galaxy, the Large Magellanic Cloud, was believed to be somewhere between 143,000 and 179,000 light years away.
Calculating the distance is important because it is “a crucial step toward establishing the size (and age) of the universe,” he said. By using that figure, scientists will be able to determine the exact distance to pulsating stars, called cepheids, in the Large Magellanic Cloud. Knowing that, they will be able to extrapolate and determine the distance to other cepheids scattered throughout the universe.
Since many cosmological theories depend on the size of the universe, scientists have long awaited a precise measurement such as the one provided by Hubble. It should mean that, within a few years, scientists will no longer have to estimate the age of the universe as somewhere between 10 billion and 20 billion years.
