On the morning of Feb. 23, 1987, a couple of dozen subatomic neutrinos zinged through specially instrumented underground sensors in Japan, Ohio and Russia. The particles had squirted from the core of a collapsing star 163,000 light years away in a small galaxy known as the Large Magellanic Cloud. They were the heralds of doom.
On their heels, a couple of hours later came a rising blitzkrieg of light, heat, x rays, shock waves, and rings and knots of gas and all manner of radiation across the electromagnetic spectrum—all the panoply of a star devouring itself in one of the great cataclysms of nature, a supernova explosion.
SN1987A, as it is known, was the nearest supernova to be discovered since humans started using telescopes, and it sent astronomers rushing to observatories in Chile and Australia where the star was dying straight overhead. Since then, it has been studied by telescopes in space and on every continent, including Antarctica. And the show is still going on, as can be seen in new images obtained by the Hubble Space Telescope and released in honor of the event’s 30th anniversary.
“There’s the shredded star in the center, the circumstellar ring that looks like a string of pearls,” says Robert Kirshner, a longtime Harvard professor and currently science program director for the Moore Foundation, who has studied the supernova for 30 years.
At its peak, SN1987A was radiating more energy than 100 million suns and was visible to the naked eye. Among other things, astronomers traced the explosion to a blue supergiant star that has now disappeared. The observations have allowed scientists to recreate the steps by which it started coming apart tens of thousands of years before the final cataclysm.
The data confirmed that most of the light from the supernova was caused by the decay of radioactive cobalt produced as the star shrank catastrophically and then rebounded even more catastrophically in a thermonuclear fury.
But another mystery remains. According to theory, the emission of neutrinos should have meant that the core of the doomed star was collapsing into a neutron star, a ball about the size of Manhattan but dense as an atomic nucleus, whose magnetic fields spinning and sweeping space like a lighthouse beam produce the clocklike signals known as pulsars. But there is no sign that a neutron star has been seen yet.
“We’ve looked, but we don’t see any little dot in the center,” Dr. Kirshner said. Maybe it is hidden by dust, or maybe enough star material fell back onto the star to nudge it into collapsing into a black hole. The end of the story of this star is still unwritten.
“The most interesting thing to test is whether we understand correctly how a star explodes and which elements it forms, by looking directly at the shredded star,” Dr. Kirshner said. “After all, you and the Earth are made of five-billion-year-old supernova debris.”