(4 of 12)
Those early characteristics lead Williams to speculate that 1987A "may have had an antecedent star that was not that massive, as supernovas go." By comparing the supernova's position with older photographs of the Large Magellanic Cloud, many astronomers at first identified a hot blue supergiant star, called SK-69 202, as the probable progenitor of 1987A. But that conclusion troubled everyone; theory holds that a star with these characteristics is too young to expire in a final explosion. Two weeks ago, as the initial ultraviolet radiation from the blast began to die down, the astronomers breathed a collective sigh of relief: ultraviolet scans indicated that the blue star might still be intact. Says Catharine Garmany, an astronomer at the University of Colorado: "It is probably shaking in its boots, but we're beginning to think it's still there." The scientists shifted their attention to two nearby, somewhat fainter stars visible on older plates. But these choices also worried them, because the progenitor should have been much brighter.
At least one of the events predicted in theory apparently occurred. All four neutrino detectors recorded the arrival of bursts of the elusive little particles -- before the light appeared.
Fascination with supernovas is hardly confined to modern science. Like today's astrologers, ancient civilizations believed the stars had a direct influence on earthly affairs, and the Chinese, who carefully recorded any changes in the sky, were especially impressed by "guest stars." They regarded such astronomical visitors as omens of important events on earth. What may be the earliest Chinese record of a supernova is an inscription on a bit of bone, dating from about 1300 B.C., that describes a bright star appearing near the star now known as Antares.
While there is some question whether this and several other of the earliest recorded sightings involved actual exploding stars, there is little doubt about the guest star of A.D. 185. "Second year of the Chung-p'ing reign period," reads an ancient Chinese text, "tenth month, day kuei-hai, a guest star appeared within nanmen. It was as large as half a mat; it was multicolored, and it scintillated. It gradually became smaller and disappeared in the sixth month of the year after next." The description, especially concerning the brightness and slow fade of the star, seems to confirm the appearance of a supernova.
Ancient records indicate that the Chinese spotted five more supernovas in the next millennium, all in the Milky Way galaxy, and some of these starbursts were also noted by other cultures. The brilliant supernova of A.D. 1006 was seen and described by an Egyptian scribe named Ali ibn Ridwan and by European monks. The exploding star of 1181 was noted by the Japanese. But it is the supernova of July 4, 1054, which suddenly blazed in the constellation Taurus, near Orion, that is perhaps most significant to present-day astronomers. It exploded only about 6,000 light-years away and left behind the slowly writhing, gradually expanding and delicately beautiful cloud of glowing gas known as the Crab nebula. Studies of the structure and dynamics of the Crab have provided modern astronomers with important insights into supernova explosions.