Spectacle Of Cosmic Surprises

By Dick Thompson

"It's a gorgeous red object against the silver gray of the Large Magellanic Cloud," said Robert Garrison of the University of Toronto. Ever since it burst into view in the southern hemisphere on Feb. 23, Supernova 1987A, the brightest exploding star in 383 years, has fascinated astronomers and astrophysicists. Its surprising behavior has prompted them to rethink how massive stars evolve and what forces rage within them. "This is how science is done," said an exultant Garrison. "There is discovery, then wild speculation, then a settling of accounts."

Last week, as 700 members of the American Astronomical Society met in Vancouver to compare notes, they were still racing to keep up with a blizzard of new data and developments on the supernova. Among them:

-- The star that exploded to create Supernova 1987A has been identified as Sanduleak-69 202, a blue supergiant whose position in the Large Magellanic Cloud neatly coincided with the supernova. Though Sanduleak was suspected, some astronomers, like Harvard's Robert Kirshner, at first thought that satellite data on the LMC showed the star still existed after the blast and thus could not have been the progenitor. Later other scientists examining the same evidence failed to locate SK-69 202. Admitted Kirshner last week: "It was that star that blew up -- no matter what you've heard elsewhere . . . from me." His colleagues guffawed.

But why would Sanduleak, a blue supergiant, a star presumably in mid-life, collapse so violently? According to theory, only aging red supergiants, whose outer gaseous layers had turned from blue to red as they expanded and cooled, spawned this type of supernova. One hypothesis: SK-69 202, like other stars in the LMC, contained relatively little metal, which theorists now think may keep the outer shell of even older stars from expanding fully, thus making it glow blue rather than red as it plunged toward its thermonuclear crisis. Said University of Chicago Astrophysicist David Schramm: "It's clear that while the core of the star is understood well, the surface is not."

-- Scientists are puzzled by the unusual pattern of light 1987A is emitting. Said Garrison: "This is not like any supernova we've yet seen." Generally, light from supernovas is expected to peak quickly and then decline. But 1987A's brightness rose, then leveled off, then increased again, peaking around May 22, when it was easily visible to the naked eye. Since then it has been gradually dimming. One possible explanation was proposed by Astronomer Stan Woosley of the University of California at Santa Cruz. He suggests that the decay of radioactive elements within 1987A's cloud of debris is now generating the light. If he is right, gamma-ray emissions from decaying cobalt 56 should start showing up this summer. Concedes Woosley: "I'm out on a limb." A more radical theory, put forth by Princeton Astrophysicist Jeremiah Ostriker, proposes that the neutron star that formed at 1987A's center when Sanduleak exploded has turned into an extremely rapidly rotating pulsar that is leaking energy and illuminating the surrounding debris.

Perhaps the most confusing phenomenon of all is the discovery of a glowing companion to the supernova that is 100 times as bright as Sanduleak had been. Scientists are frankly stumped by its appearance. Two teams of astronomers, from the Harvard-Smithsonian Center for Astrophysics and London's Imperial College, both using a technique known as optical speckle interferometry (quickly dubbed "that speckled thing"), fed data from telescopic observations into computers. What emerged was a composite picture that confounded everyone. Said Woosley: "It's easier to say what it isn't than what it is. It wasn't there before the supernova. It's not a star. It's not a second supernova. I would quit astronomy and go live on a mountain as a hermit if two supernovas went off at the same time that close together." Cracked University of Colorado Astrophysicist Richard McCray: "Once again, nature has been more imaginative than the astronomers."

As its multiple layers cool and become transparent, Supernova 1987A continues to tantalize scientists. What will be revealed? "Eventually," said Woosley, "we should see the monster that lives at the center." Predicted McCray: "The best is yet to come."

With reporting by J. Madeleine Nash/Vancouver