Pulsar ages may need refiguring.New images taken with the Chandra X-Ray Observatory have confirmed recent evidence that a known pulsar, a rapidly spinning neutron star neutron star, extremely small, extremely dense star, about double the sun's mass but only a few kilometers in radius, in the final stage of stellar evolution. Astronomers Baade and Zwicky predicted the existence of neutron stars in 1933. In the central core of a neutron star there are no stable atoms or nuclei; only elementary particles can survive the extreme conditions of pressure and temperature., was born in a supernova supernova, a massive star in the latter stages of stellar evolution that suddenly contracts and then explodes, increasing its energy output as much as a billionfold. Supernovas are the principal distributors of heavy elements throughout the universe; all elements heavier than iron are produced in supernovas. Supernovas also are the principal heat source for interstellar matter and may be a source of cosmic rays. explosion that Chinese astronomers witnessed in A.D. 386. The finding, which indicates the pulsar is much younger than earlier calculations suggested, calls into question how astronomers traditionally compute the ages of these rapidly rotating, ultracompact stars. The finding also represents only the second time that a pulsar has been definitively linked to a supernova observed centuries ago, notes Victoria M. Kaspi of McGill University in Montreal. Scientists had previously established a clear link between the Crab nebula Crab Nebula, diffuse gaseous nebula in the constellation Taurus; cataloged as NGC 1952 and M1, the first object recorded in Charles Messier's catalog of nonstellar objects. It is the remnant of a supernova that was observed in 1054 by Chinese and Arab astronomers to be as bright as Venus; markings in northern New Mexico depict a star near a crescent moon that might be a record of this supernova. pulsar and a supernova sighting in China in A.D. 1054. Observations in 1997 with Japan's ASCA ASCA - Adult Survivors of Child Abuse ASCA - Advanced Satellite for Cosmology & Astrophysics ASCA - Advanced Spacecraft for Cosmology Astrophysics ASCA - Air Support Coordination Agency ASCA - Airplane Stability and Control Analyzer (Whirlwind) ASCA - Alberta Sporting Clay Association ASCA - American Safe Climbing Association ASCA - American School Counselor Association ASCA - American Society of Consulting Arborists satellite indicated that a known pulsar coincides with the position of the A.D. 386 supernova remnant G11.2-0.3. But it took the sharper eye of Chandra to reveal that the pulsar lies at the exact core of the remnant. "This makes the association between the pulsar and the supernova remnant essentially inescapable," says Kaspi. It also pegs the pulsar's age at just over 1,400 years. From the pulsar's current rotation rate and a model of how rapidly it slows over the years, astronomers had calculated its age as 24.000 years. If the pulsar were really that old, it would have had enough time to migrate far from the supernova's core, Kaspi adds. To explain the discrepancy between the actual and calculated ages, the pulsar must have started with a slower rotation than the standard model assumes, Kaspi says. The new findings, along with a similar age discrepancy on another pulsar found by a different team, suggest that pulsar ages derived from their assumed rate of spin down "can be even more deceptive than we had previously thought," says Andrew S. Fruchter of the Space Telescope Science Institute in Baltimore. "It is the difficulty of determining true pulsar ages ... [that] makes these historical associations [with supernova remnants] so valuable," he notes. |
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