In 1181 a rare explosion lit up the sky, and we may have finally found what it left behind

For 900 years, scholars and stargazers have sought to explain a bright cosmic object that briefly lit up the skies above China and Japan in 1181 CE. A new study may have solved the mystery at long last.

The nebula Pa 30 – named Parker's Star, one of the hottest in the Milky Way – and the star it surrounds are a match for the phenomenon observed in the sky all those years ago, according to measurements of its modern-day position, expansion speed, and state.

Observations show that the cloud of gas and dust that is Pa 30 is expanding at a rate of 1,100 kilometers (684 miles) per second. That suggests it originated from a central point about 1,000 years ago, most likely from a supernova explosion. This may well be what was observed by contemporary astronomers back in 1181.

"The historical reports place the guest star between two Chinese constellations, Chuanshe and Huagai," says astrophysicist Albert Zijlstra from the University of Manchester in the UK. "Parker's Star fits the position well. That means both the age and location fit with the events of 1181."

The stargazers of the 12th century reported an object in the sky as bright as Saturn that was visible for six months. They also made records of its position in the sky.

Astronomers have since used those observations to come up with a few hypotheses but haven't been able to confidently pinpoint what it left behind – until now.

Pa 30 and Parker's Star are thought to have been created by the merger of two small, dense white dwarf stars, a rare occurrence leaving behind what's known as a Type Iax supernova, or zombie star.

It's a rare category of supernova that scientists are still learning more about. What's even rarer is having information about how the supernova started, as well as the remnant that's now left behind.

"Only around 10 percent of supernovae are of this type, and they are not well understood," says Zijlstra. "The fact that SN1181 was faint but faded very slowly fits this type. It is the only such event where we can study both the remnant nebula and the merged star and also have a description of the explosion itself."

Since 1006 CE, there have only been five bright supernovae spotted in the Milky Way, and astronomers have already found matches for the other four. One of them, now known as the Crab Nebula in the Taurus constellation, is also thought to be around a thousand years old.

First discovered in 2013, it seems that Pa 30 now completes the set.

Before now, there had been some debate about whether the merger of two white dwarf stars could result in a supernova like this, so the discovery has plenty to teach astronomers about other similar supernovae too.

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

The research has been published in the Astrophysical Journal Letters.

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