Pulsar ages may need refiguring.New images taken with the Chandra X-Ray Observatory Chandra X-ray Observatory U.S. X-ray space telescope. It was named after astrophysicist Subrahmanyan Chandrasekhar and was launched into orbit in 1999. Its mirror, with an aperture of 1.2 m (4 ft) and a focal length of 10 m (33 ft), produces unprecedented resolution. have confirmed recent evidence that a known pulsar pulsar, in astronomy, a neutron star that emits brief, sharp pulses of energy instead of the steady radiation associated with other natural sources. The study of pulsars began when Antony Hewish and his students at Cambridge Univ. , 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. , was born in a supernova 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 McGill University, at Montreal, Que., Canada; coeducational; chartered 1821, opened 1829. It was named for James McGill, who left a bequest to establish it. Its real development dates from 1855 when John W. Dawson became principal. 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. pulsar and a supernova sighting in China in A.D. 1054. Observations in 1997 with Japan's ASCA ASCA American School Counselor Association ASCA Australian Shepherd Club of America ASCA Arab Society of Certified Accountants ASCA American Swimming Coaches Association ASCA American Society of Consulting Arborists ASCA Association of State Correctional Administrators 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 The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST; in orbit since 1990) and for the James Webb Space Telescope (JWST; scheduled to be launched in 2013). 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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