Now it is known what caused the strange light in the sky about 900 years ago

Remained a mystery for 840 years, now it has been discovered what had caused it: the "blame" would be two stars. In the 12th century, Chinese and Japanese astronomers had spotted a light as bright as Saturn.

The cause of the origin of a strange light, which Chinese and Japanese astronomers spotted in the sky in the 12th century, remained shrouded in mystery for 840 years. Its brightness was equal to the brilliance of Saturn and, at the time of the sighting, had been identified as a powerful stellar explosion known as a supernova whose approximate location had been marked. Now astronomers have solved the riddle of what caused it: it would have been the collision in the Milky Way of two extremely dense stars that gave rise to the supernova.

The origin of the strange light in the sky

The explosion probably caused the formation of a red-hot star, now known as Parker's star, and a nebula, an expanding shell of gas and dust, called Pa 30. This supernova, or the so-called Chinese Guest Star, from 1181 A.D. (which remained visible from Aug. 6 to Feb. 6 of that year) is just one of nine supernovae historically recorded in our galaxy, according to the study, published in The Astrophysical Journal Letters. Astronomers have identified the remains of only a handful of these supernovae, but the Chinese Guest Star was the only supernova from the last millennium whose remains had not yet been found.

Astronomers discovered the Pa 30 nebula in 2013. So, in the new study, the researchers calculated the expansion speed of Pa 30. They found that it was inflating at a rate of 1,100 kilometers per second. Knowing this speed, they calculated that the nebula must have originated about 1,000 years ago, which would place its origins around the time the ancient supernova appeared. The researchers also had historical documents describing the star. "Historical accounts place the Guest Star between two Chinese constellations, Chuanshe and Huagai. Parker's star fits the location well," Albert Zijlstra, a professor of astrophysics at the University of Manchester in the United Kingdom, said in a statement. "This means that both the age and location match the events of 1181." Previously, researchers had proposed that Pa 30 and Parker's star were the result of the merger of two white dwarfs, extremely dense stars that have used up all their nuclear fuel. Such mergers lead to a relatively faint and rare type of supernova known as a lax-type supernova.

According to Zijlstra, the 1181 AD supernova was faint and faded very slowly, which suggested it was likely a lax-type supernova. "The combination of all this information - such as the age, the location, the brightness of the event and the historically recorded duration of 185 days" suggests that Parker's star and Pa 30 are the remnants of this ancient supernova, Zijlstra said. The 840-year-old strange light would thus be the only known lax-type supernova for which astronomers can conduct detailed studies.

Regarding stars, another study has identified that white dwarfs are able to slow theirĀ aging process.

Stefania Bernardini