The Crab Nebula is a child with many fathers. It is the remnant of a stellar explosion, a supernova, in the constellation of Taurus. A supernova is At a distance of some 6,500 light years from earth, this 11 light year diameter stellar light show is one of the most consistent sights in our night sky. It is currently expanding outward at about 1,500 kilometers per second, and its outward velocity is believed to have accelerated since the explosion that created it. The origin, or progenitor star that created the Crab Nebula, is thought to have been a massive star which ran out of fuel and collapsed in on itself, reaching such tremendous temperatures that it explodes. This has been determined by the presence of a pulsar in the nebula, which is only caused by the collapse of a massive star.
Theoretical models of supernova explosions indicate that the progenitor star for the Crab Nebula must have been between 9 and 11 solar masses. Stars of smaller solar mass would have produced a planetary nebula, and those with a larger mass would have an entirely different composition
John Bevis first reported observing the nebula in 1731, and it was rediscovered (though one might aruge that it wasn’t lost, just that people didn’t know where to look for it) by Charles Messier in 1758. He catalogued it as the first entry in his listing of comet-like objects. In 1840, the Earl of Rosse, observing from Birr Castle, viewed the nebula. Because a drawing of the object he made looked like a crab, he named it the Crab Nebula.
In the early 20th century, astronomers analyzing early photographs of the nebula taken several years apart, discovered that it was expanding. Backtracking, they came to the conclusion that the nebula must have been visible from earth about 900 years earlier. Further research revealed that Chinese and Arab astronomers had observed the supernova in 1054, and had recorded their observations. Research has indicated that the supernova that created the Crab Nebula probably appeared in April or May of that year, and would have been visible to the naked eye for up to two years. The Asian and Middle Eastern observations occured in the same part of the sky as the phenomenom seen by later European astronomers. The conclusion, therefore, is that the Crab Nebula was discovered in 1054 by Chinese and Arab astronomers, working independently. Starting with Bevis, what we have is simply rediscovery.
