Science: A Wonder in the Southern Sky

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By now, says Astronomer Stan Woosley of the University of California at Santa Cruz, "everyone with anything to look with is looking at it." Every optical telescope in the Southern Hemisphere is trained on 1987A; a newly launched Japanese satellite is scanning it for X rays emitted by the supernova's hot gases; the Solar Max satellite is looking for the gamma rays characteristic of very energetic explosions; and another spacecraft, the International Ultraviolet Explorer, has already made observations of the explosion's ultraviolet radiation. These indicate that the star's atmosphere, which astronomers have determined is exploding outward at a speed of about 36 million m.p.h., is already cooling. But the supernova is believed to be getting still brighter. By week's end it was as bright as 100 million suns, and soon it could match the brilliance of a billion stars.

Within a couple of weeks, says Harvard's Robert Kirshner, the temperature of 1987A's expanding shell should drop from its current 10,000 degrees C to roughly 6,000 degrees C, about the same temperature as our sun's surface. During the explosion, though, internal temperatures climbed to billions of degrees, and elements like silicon, sulfur and platinum, synthesized by the star, began spewing out over a vast region of space, where they will form clouds of gas and dust that can coalesce into new stars and planets. Indeed, most of the elements abundant on earth today, except hydrogen, were cooked up in some star that became a supernova. Says Woosley: "The calcium in our bones, the iron in hemoglobin and the oxygen we all breathe came from explosions like this one."

The first question astronomers asked: What kind of supernova is 1987A? There are two main types. A Type II explosion occurs when a massive star exhausts its nuclear fuel and collapses under its own weight. When its matter, falling in from all directions, meets at its center, a shock wave bounces back out in a tremendous explosion that blows apart the star's outermost layers. A Type I explosion occurs when a gravitationally powerful white dwarf star that is part of a binary star system draws gas from its nearby companion. When it accumulates too much, reaching a critical mass about 1.4 times as great as our sun's, it blows up.

Astronomers think 1987A is probably a Type II. But a star called SK 202-69, visible in older photographs in almost exactly the supernova's position and therefore possibly the star that exploded, is a blue supergiant, rather than the red supergiant predicted by theory. Astronomers are still looking for evidence of a previously undetected red supergiant in the same area. "There's a lot of confusion," says Arnett. "We have had so little data on supernovae. We have pieces of the puzzle, but they don't all fit together the same way."

The chance that they might finally be able to pinpoint a specific progenitor star, which could finally confirm or recast their theories about how supernovas explode, has astronomers beside themselves with excitement. "It's like Christmas," says Woosley. "We've been waiting for this for 383 years." Agrees Kirshner: "Everyone in the field has been calling each other up, partly for scientific reasons and partly for sheer pleasure. It's like when someone has a baby -- it's a great event, and you just want to talk."

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CREDIT: TIME diagram by Paul J. Pugliese