The question, why the first documented supernova was super-sized and grew so fast, has puzzled astronomers for centuries. Now it is solved by US researchers. The supernova, an exploded star, was observed in 185 A.D. and documented as a mysterious \"guest star\" by Chinese astronomers. It was visible for eight months. Scientists later found the supernova, 8,000 light years away, was a bigger-than-expected supernova remnant. BBC reported that if the infrared light it emits could be seen by human eyes, it would appear to be as large as the full Moon in the sky. Through observations in space telescopes, researchers of a latest study revealed that the explosion took place in a cavity in space, which allowed the star\'s remains to travel out much faster and farther. The study was published online in the Astrophysical Journal Monday. The supernova was \"two to three times bigger than we would expect for a supernova that was witnessed exploding nearly 2,000 years ago. Now, we\'ve been able to finally pinpoint the cause,\" stated Brian Williams, lead author of the study and an astronomer at North Carolina State University in Raleigh.