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30 years later, supernova 1987A is still sharing secrets

Ian Shelton was alone at a telescope in the remote Atacama Desert of Chile. After three hours getting a picture of the Large Magellanic Cloud, a wispy galaxy that orbits the Milky Way, he was plunged into darkness. High winds had taken hold of the rolltop door in the observatory’s roof, slamming it shut.

“This was maybe telling me I should just call it a night,” says Shelton, who was a telescope operator at Las Campanas Observatory on that evening of February 23, 1987.

He grabbed the photograph — an 8-by-10 inch glass plate — and headed off to the darkroom (yes, these were the days of developing images by hand). As a quick quality check, he compared the just-developed picture with an image he had taken the previous night.

Shelton noticed a star that hadn’t been there the night before. “I thought, this is too good to be true,” he says. He stepped outside and looked up. There it was — a faint point of light that wasn’t supposed to be there. He walked down the road to another telescope and asked astronomers there what they would say about an object that bright appearing in the Large Magellanic Cloud, just outside the Milky Way.

“Supernova” was the group’s response, Shelton says. He ran outside with the others — including Oscar Duhalde, who recalled seeing the same thing earlier in the evening — to double-check with their own eyes.

The supernova has gotten dimmer by a factor of 10 million, but we can still study it.

— Robert Kirshner

They were witnessing the explosion of a star, quickly dubbed supernova 1987A. It was the closest supernova seen in nearly four centuries and so bright it was visible without a telescope. “People thought they’d never see this in their lifetime,” says George Sonneborn, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Md.

With roughly 2 trillion galaxies in the observable universe, there’s almost always a star exploding somewhere. But a supernova close enough to be seen with the unaided eye is a rare event. In the Milky Way, astronomers estimate, one goes off every 30 to 50 years. But the most recent one seen was in 1604. At a distance of about 166,000 light-years, SN 1987A was the closest since the time of Galileo.

Supernovas are “important agents of change in the universe,” says Princeton astrophysicist Adam Burrows. They end the lives of stars and trigger the birth of new ones. They change the fate of entire galaxies by stirring up the gas needed to build more stars. Most, perhaps even all, of the chemical elements heavier than iron are forged in the chaos of the explosion. Lighter elements — “the calcium in your bones, the oxygen you breathe, the iron in your hemoglobin,” Burrows says — are created over the star’s lifetime and then spewed into space to seed a new generation of stars and planets — and life.

Thirty years after its discovery, supernova 1987A remains a celebrity. It was the first supernova for which the original star could be identified. It offered up the first neutrinos detected from beyond the solar system. Those subatomic particles confirmed decades-old theories about what happens in the heart of an explosion. And today, the supernova’s story continues to be written. New observatories draw out more details as shock waves from the explosion keep plowing through interstellar gas. “The supernova has gotten dimmer by a factor of 10 million, but we can still study it,” says astrophysicist Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics. “We can study it better and over a wider range of light than we could in 1987.”

A daily adventure

Communication was a bit slower when 1987A exploded. Shelton’s attempts to call the International Astronomical Union in Cambridge, Mass., failed. So a driver took off to La Serena, a town about 100 kilometers away, to alert the IAU by telegram.

Lots of researchers didn’t believe the news at first. “I thought, that’s got to be a joke,” says Stan Woosley, an astrophysicist at the University of California, Santa Cruz. But as word spread via telegram and telephone, it quickly became clear that it was not a prank. Amateur astronomer Albert Jones in New Zealand reported seeing the supernova the same night before clouds moved in. About 14 hours after the discovery, NASA’s International Ultraviolet Explorer satellite was already watching. Astronomers around the world scrambled to redirect telescopes both on the ground and in space.

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Telegram announces 1987A

On February 24, 1987, the International Astronomical Union sent out a telegram that started as follows:

W. Kunkel and B. Madore, Las Campanas Observatory, report the discovery by Ian Shelton, University of Toronto Las Campanas Station, of a mag 5 object, ostensibly a supernova, in the Large Magellanic Cloud at R.A. = 5h35m.4, Decl. = -69 16’…

In astronomy lingo, the telegram provided the brightness (magnitude 5) and coordinates (R.A. for right ascension and Decl . for declination) of the supernova in the Large Magellanic Cloud, shown before (left) and after the explosion (right).

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