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Physics LibreTexts

13.27 Seeing the Death of a Star

Oscar Duhalde tilted his head back and looked at the night sky. Duhalde was a telescope operator at the Las Campanas Observatory in Chile, and he had stepped outside around midnight on February 23, 1987 to check the sky conditions. The observatory was in the foothills of the Andes, far from civilization, and the stars burned brightly on a backdrop as black as velvet. He noticed a new star near the 30 Doradus nebula in the Large Magellanic Cloud, which is a nearby galaxy named by the explorer Magellan on his first southern voyage. Since the star had not been there on previous nights, it must have brightened sharply. It was a delicious moment of discovery. This was the first supernova bright enough to be seen by the naked eye for nearly 400 years! Duhalde was probably the first human witness to the death of this particular star, in an extraordinary and violent event called a supernova.

 

Astropedia Image
Supernova 1987A. Click here for original source URL

Astropedia Image
Supernova 1987A Timelapse. Click here for original source URL.

The astronomical community spun into a whirlwind of activity. At Las Campanas, Ian Shelton developed a photograph of 30 Doradus that he had already taken and so was credited with recording the discovery (the first of the year, so designated SN 1987A). The supernova was independently spotted by an amateur astronomer working in New Zealand; several other amateurs missed making the first observation due to clouds at their observing sites. Around the world, telescopes took spectra of the dying star, and satellites recorded its high-energy emission.

The first trace of the supernova was not the dazzling light, however, but an invisible wave of neutrinos that passed through the Earth. In Japan, researchers at a particle detector 3000 feet underground sifted through their data and found 11 events caused by interactions between neutrinos and the 2100 tons of highly purified water that filled their detector. The detection of these ghostly particles from the death throes of an object beyond our own galaxy ironically heralded the birth of a new field of astronomy.

SN 1987A went off in a neighboring galaxy to the Milky Way. In fact, we are overdue for a supernova in our own galaxy; the expected rate is one per century. If that happened, it would likely be at a distance of several thousand light years, a hundred times closer than SN 1987A. By the inverse square law, it would be an event tens of thousands of times brighter. Ironically, at peak brightness a supernova in our own galaxy might be too bright for major telescopes to observe without saturating their CCD detectors, so they would have to partially close their missor covers or insert filters in the optical path. for amateur astronomers it would be a field day! These are once in a lifetime events for astronomers. 

Early Homo Sapiens were just developing the first societies on the plains of Africa when the blue super giant in the Large Magellanic Cloud exhausted its nuclear fuel. The subsequent core collapse triggered a prodigious explosion. A flood of radiation and neutrinos poured into space, in a sphere expanding at the speed of light. Nearly 160,000 years later, just after we developed the tools of modern astronomy, that sphere swept across the Earth's path. SN 1987A offers a wonderful opportunity to check our theories of how a star ends its life. We also have ringside seats for the formation of the exotic object that is left behind when a massive star dies.