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2,000-year-old stellar mystery solved

CAPE CANAVERAL, Fla. - Astronomers finally know why the first documented supernova was super-sized.

The exploded star was observed by the ancient Chinese in the year 185, and visible for eight months. It was later found to be a bigger-than-expected supernova remnant, 8,000 light years away.

New observations in the infrared show the explosion took place in a cavity in space. Researchers said that this "hollowed-out cavity" of space was relatively free of gas and dust, thus allowing the stellar shrapnel to shoot faster and farther out into the universe.

The star - similar to our sun - died peacefully and turned into a dense white dwarf. It sucked up material from another star, and then exploded in a supernova.

NASA announced the findings Monday. Four space telescopes were used in the study.

NASA's Spitzer Space Telescope and the Wide-field Infrared Survey Explorer were used to take infrared views of the supernova.

What caused the explosion nearly 2,000 years ago. Astronomers now believe what the locals saw was a Type Ia supernova, in which an otherwise-stable white dwarf, or dead star, got pushed beyond the brink of stability when a companion star dumped material onto it.

"This supernova remnant got really big, really fast," said Brian Williams, an astronomer at North Carolina State University in Raleigh, in a statement. "It's two to three times bigger than we would expect for a supernova that was witnessed exploding nearly 2,000 years ago. Now, we've been able to finally pinpoint the cause."

Another view of RCW 86, the dusty remains of the oldest documented example of an exploding star, or supernova NASA/JPL-Caltech/UCLA
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