900-year-old Chinese supernova mystery points to strange nebula

In the year 1181 AD, a new bright point of light as luminous as the planet Saturn appeared to Chinese and Japanese skygazers for a little more than six months before disappearing. Hundreds of years later, researchers believe they have finally found the source of this mysterious appearance.

The event, like the famous Crab Nebula-forming stellar explosion of 1054, is one of just a handful of bright nearby flashes noted in historical records, but unlike the Crab Nebula, the 1181 spectacle was tricky to pin down.

The historical record leaves a few clues that have been useful to modern astronomers. First, the timing: this “guest star” shined for 185 days, from Aug. 6, 1181, to Feb. 6, 1182. The record also indicates its place in the sky, which was a spot located between two Chinese constellations, Chuanshe and Huagai, near the modern Cassiopeia.

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These cosmic puzzle pieces led a research team to the ancient flash’s likely culprit: a supernova whose remnants now form a fast-expanding nebula called Pa30. The nebula’s clouds move so quickly that, in the new research, scientists from Hong Kong, the U.K., Spain, Hungary and France found that Pa30’s dust and gas could travel the distance from Earth to the moon in a whopping five minutes. By using that speed and calculating backward, the researchers determined that the nebula would fit a supernova that exploded around 1181.

The team found that Pa30 formed from a rare and relatively faint type of supernova, called a ‘Type Iax supernova.’ “Only around 10% of supernovae are of this type and they are not well understood. The fact that SN1181 was faint but faded very slowly fits this type,” Albert Zijlstra, an astrophysicist at the University of Manchester in the U.K., said in a statement about the new research. 

Scientists also found that Parker’s star, one of the hottest stars in the Milky Way, is also a likely counterpart to the supernova. The nebula and the star are thought to be the result of a massive collision and subsequent merger of two dim stellar corpses known as white dwarfs. 

“This is the only Type Iax supernova where detailed studies of the remnant star and nebula are possible,” Ziljlstra added. “It is nice to be able to solve both a historical and an astronomical mystery.”

The study was published on Wednesday (Sept. 15) in the journal Astrophysical Journal Letters. 

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