Since the beginning of history, humanity has documented celestial events. Chinese astronomers have been particularly good at recording supernovae, having cataloged 20 potential sightings over a span of 2,000 years.
One of these sightings, a bright new star seen in 386 CE, was thought to be the cause of the gorgeous supernova remnant G11.2-0.3, but the latest observations from NASA’s Chandra telescope indicate that this is not the case. Although this supernova formed between 1,400 and 2,400 years ago (from our point of view), it would have been too faint to be visible.
Chandra had observed the object in 2000, 2003, and 2013, which allowed the researchers from North Carolina State University and New York University Abu Dhabi to estimate precisely how quickly the nebula left over from the supernova is expanding.
In a paper, published in the Astrophysical Journal, the team estimates that the stellar material is moving at a speed between 700 and 1,100 kilometers (435 to 680 miles) per second.
Although it might not have been documented historically, G11.2-0.3 is still a very special object. It is believed to be one of the youngest known examples of a core-collapse supernova. These types of stellar explosion happen at the end of a star’s life, when the star is not releasing enough energy to balance out its mass, and it collapses under its own weight.
The collapse is catastrophic. The core is compressed so much that it forms a pulsar, a rapidly-spinning neutron star, and the release of energy blows the outer layers of the star apart to form a nebula.
In the case of G11.2-0.3 the nebula looks very circular, but astronomers were able to show that appearances are deceptive. The gas is moving unevenly. The scientists think the explosion was quite uneven, but subsequent stellar winds either from the pulsar or from a companion star helped speed up some of the gas, and the nebula ended up looking very symmetric.
So the supernova seen in 386 CE goes back to being an unproven observation, but G11.2-0.3 is definitely one for the history books.