Pulsars much older than thought, astonomers say

July 11, 2000

New measurements throw theory into doubt

Pulsars -- spinning, superdense neutron stars that emit powerful beams of radio waves and light -- may be much older than scientists thought, according to researchers using measurements made with the National Science Foundation's (NSF) Very Large Array (VLA).

Bryan Gaensler of the Massachusetts Institute of Technology and Dale Frail of NSF's National Radio Astronomy Observatory in New Mexico used the VLA radio telescope to study a pulsar previously thought to be 16,000 years old. They found that the pulsar is at least 40,000 years old and may be as old as 170,000 years. The results of their research will appear in the July 13 issue of Nature.

"The signals from a spinning pulsar are as regular as an atomic clock, and for three decades we have relied on them to estimate the age of pulsars," said Morris Aizenman, NSF senior science advisor. "These new measurements indicate we've been wrong about the age of a pulsar, challenging the standard theory of how pulsar signals are produced."

Stars much more massive than the sun end their lives in violent supernova explosions, leaving behind extremely dense neutron stars. Some of these neutron stars produce the beams of electromagnetic radiation that characterize pulsars. Gaensler and Frail calculated the speed of pulsar B1757-24, located 15,000 light years away in the constellation Sagittarius, which had traveled outside the shell of debris from the supernova explosion that created it. This pulsar and shell, together known as a supernova remnant, are dubbed "the Duck" because of their unusual appearance.

For the pulsar to have traveled from the center of the supernova remnant to its present position in 16,000 years, it would have had to move at about 1,000 miles per second. By comparing a 1993 VLA image of the region to one they made last year, the scientists calculated the pulsar's speed to be no more than 350 miles per second.

"This means the pulsar took much longer to reach its current position, and so it is a much older object than we had believed," said Frail. "This pulsar has been lying to us about its age." The discrepancy could require astronomers to re-examine many of their previous conclusions about neutron stars and how they work. The implications could also extend beyond astronomy to particle physics.

"Neutron stars, as the densest objects in the universe, provide a unique laboratory for physics," said Gaensler. "Physicists look at neutron stars as a way of showing how matter acts under these extreme conditions. Part of what they need to know in order to draw proper conclusions is the age of the neutron star. If that changes, so do many of their theories."
NSF PR 00-49

Media contact: Amber Jones 703-306-1070 aljones@nsf.gov

Program contact: Jim Breckinridge 703-306-1833 jbreckin@nsf.gov

Editors: For embargoed images, see: http://www.aoc.nrao.edu/pr/duck.html

National Science Foundation

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