(9 of 12)
Another question that troubled some astronomers was why 1987A stopped brightening. To be sure, some previously observed supernovas have leveled off in brightness for a time, then shot up to the expected brilliance. In fact, last week southern hemisphere observatories reported that the supernova's magnitude, which had remained relatively constant for almost two weeks, showed signs of increasing slightly, from 4.5 to 4.25. But even if 1987A stays "subluminous," it will be important because it may point to the existence of a previously unknown class of stellar explosion.
What does it all mean? "There will be as many notions of what's going on as there are astronomers," says Woosley. "It's what you might call organized scientific chaos. When it's all over, we'll have a better idea of what causes a supernova, but the one rule now is that you shouldn't trust the theoreticians. Expect the unexpected."
Still, the theoreticians could crow that in at least one way 1987A had performed according to the script. Minutes after hearing about the supernova but before they learned of any neutrino data, Astrophysicist Bahcall and two Israeli colleagues began working on a paper predicting the number of supernova neutrinos that should have been recorded by various detectors on earth; their paper was published in last week's Nature. If the neutrinos had been recorded -- and especially if they arrived before the supernova was seen -- it would be a dramatic confirmation of current supernova theory.
Sure enough, a check of the Kamiokande II detector in Japan disclosed that a burst of eleven neutrinos, with the predicted range of energies, arrived in a span of 13 seconds on Feb. 23, about three hours before light from the supernova was first observed. And data provided by the IMB (Irvine-Michigan- Brookhaven) detector under Lake Erie showed a burst of eight neutrinos in six seconds at the same time as the Japanese reading. Says Physicist Frederick Reines, of the University of California, Irvine: "One observation by one team is not sufficient; it has to be confirmed by an independent group. But together, the results from the IMB detector and the Kamiokande II detector are hard to disbelieve."
Both the Mont Blanc and Mount Elbrus detectors also picked up neutrino bursts at the crucial time, but scientists are still puzzling over another burst recorded at Mont Blanc some 4 1/2 hours earlier. They will examine the data further this week at a meeting in Wisconsin. In any case, Bahcall is ecstatic. "I think this is almost surrealistic," he says. "It's hard to believe I'm actually awake." Agrees University of Chicago Astronomer W. David Arnett: "There have been smoking guns, but we've never seen the act committed before."
The neutrino bursts could help pin down theoretical models not only about how stars die but also about how the universe might expire. A debate is raging over how much "dark matter" -- stuff invisible to astronomers -- exists in the universe. If there is sufficient dark matter, its gravity will be enough to force the universe, still expanding from the Big Bang, to slow, stop and fall together again in a "Big Crunch." If the necessary matter does not exist, the universe will expand forever.