A Mysterious Object Lit Up the Sky 600 Years Ago. Astronomers Finally Found It.

Yahoo

5 hours ago

Here's what you'll learn when you read this story:
In 1408, Chinese astronomers and court officials observed an especially bright object in the sky that appeared for about ten days, but its identity remained unknown.
The object was described as yellow (an auspicious color, even thought it might have actually been any color besides red) and smooth (stars with rays were seen to be unlucky because of the sharp edges).
It was determined that the object was a classical nova, and according to recent work, it could be a stellar remnant in the Vulpecula constellation.
At dusk on a late October night in 1408, something mysterious lit up the skies above China. Ming Dynasty astronomers who recorded the phenomenon wrote that its brightness was intense enough to last at least ten days. Back then, it was thought to be a 'celestial guest'—a lost star that had wandered into that region of sky.
Observed near the Niandao asterism (a pattern of stars that isn't technically a constellation, like the Big and Little Dippers), in the same area as the Cygnus and Vulpecula constellations, the 'guest star' was seen as an auspicious Zhou Bo Virtue Star. These stars were intensely bright and believed to manifest when an emperor brought peace and harmony to the realm. Astronomer Hu Guang wrote a congratulatory memorial of this event to the emperor, describing the object as 'smooth and bright' with 'a pure yellow color.'
'The heavenly vault reveals its blessings, with the Virtue Star's glittering brilliance in the middle of the sky; the Silver River [Milky Way] unfolds its splendor, its luminous beauty interwoven along the Niandao. This splendid omen is truly a sign of an enlightened era,' Hu said in his Memorial of Congratulations on the Auspicious Star.
617 years later, what exactly this object was had still not been determined, but astronomer Boshun Yang was determined to find out. He and his team carefully studied the ancient observations of the guest star, which had been meticulously written down to honor the emperor. Superstition held that stars that were smooth and round (as opposed to those with rays, whose appearance of points and spikes, or mang jiao was thought of as a bad omen) were good luck. The use of the word 'luminous' in descriptions conveys the brightness of an object that might have had rays without being ominous.
The star was also described as 'yellow in color,' most likely because yellow has positive associations. Whether it really was yellow is debatable. Many stars appear somewhere between bluish and pure white in color, but those colors were also considered unlucky, There were also fewer terms for color in the ancient world, with many languages using only one term for greens and blues, and having no words for shades between red, orange, and yellow. An earlier supernova, for instance, was described as whitish-blue in Japan but yellow in China.
'Celestial omens are assumed to have been highly important; we can consider the information reliable,' Yang and his team said in a study recently uploaded to the preprint server arXiv.
Yang thinks that the apparition could have been any color except red, which in this case would have been caused by extinction—the reddening of light caused by the presence of interstellar dust (red tends to dominate in extinction, as shorter wavelengths like blue are drowned out more easily than longer wavelengths like red). Niandao was 'in the middle of the sky,' so extinction was unlikely.
So, what kind of object had the Chinese court officials and literati really seen centuries ago? It couldn't have been a comet, since it would have not been visible for such a long period of time. The objects seen as 'guest stars' at the time of these writings were actually stellar transients—temporary phenomena, like supernovae, that occur due to a change in the star.
Yang thinks that the object described by these documents is an example of a classical nova, rather than a supernova. Novae typically happen in binary systems consisting of a white dwarf (the compact core of a dead intermediate-mass star like our Sun) and a 'living' red giant star. The white dwarf's powerful gravity pulls in hydrogen from its companion, and enough eventually accumulates to light up the surface of the white dwarf. As the white dwarf keeps drawing hydrogen and helium, it triggers nuclear fusion reactions that create heavier elements, and the energy released by those reactions releases so much energy that it creates the nova.
Because the object's light curve (compared to the cup of an oil lamp), brightness, and visibility were all consistent with what one would see in a nova, Yang and his team concluded this particular type of explosion is what must have been spotted in the sky all those years ago. Even better, they believe they may know the exact object that put on the light show—the stellar remnant CK Vul in the constellation Vulpecula.
'The 1408 even stands as one of the earliest well-documented nova candidates, offering a rare opportunity to probe pre-telescopic stellar phenomena,' the team wrote. 'Future high-resolution observations of CK Vul's remnant […] could test the hypothesized connection to the 1408 eruption.'
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