In the spring of 386 A.D., Chinese astronomers made note of a new star, most likely a supernova, in the sky near Sagittarius, as the constellation later came to be known. Its remnants¿an expanding ring of gas and particles¿were found in the 1970s and named G11.2-0.3. Now a group of Canadian researchers report that a pulsar in the area is probably left over from the historic event as well. Using NASA's Chandra X-ray Observatory, Victoria Kaspi and her colleagues at McGill University discovered that the pulsar, a neutron star originally spotted in 1997, lies at the exact geometric center of G11.2-0.3. They described their finding last week at the American Astronomical Society meeting in San Diego.

The pulsar's precise location suggests that it was created during the fourth-century explosion. If so, it is only the second such star associated with a recorded supernova: the Crab Nebula is believed to have resulted from the supernova in 1054 A.D. Based on the pulsar's spin rate of 14 times per second, scientists at the Japanese Advanced Satellite for Cosmology and Astrophysics (ASCA) estimated its age to be roughly 24,000 years old. But if it is truly 1,615 years old, as the new research suggests, then pulsars may spin more slowly than was expected. "We believe that the pulsar and the supernova remnant G11.2-0.3 are both likely to be left over from the explosion seen by the Chinese observers over 1,600 years ago," says Mallory Roberts of McGill University. "While this is exciting by itself, it also raises new questions about what we know about pulsars, especially during their infancies."