The Crab Nebula has only been studied by astronomers for about 90 years but it is one of the few astronomical objects whose origin is documented in history. It is the remnant of an immense star, about 10 times the mass of the sun, that exploded at the end of its life in a supernova. What it left behind is an expanding debris cloud of gas and dust with an ultra-dense, fast-rotating object – a pulsar – at its core. This pulsar, about the size of a city and containing about one and a half times the mass of our sun, spins on its axis 30 times every second.
The commonly accepted date of the supernova is July 4, 1054. For a while, it was the brightest object in the sky other than the sun and moon and was visible in the daytime sky for 23 days. It disappeared from the night sky almost two years later on April 17, 1056. The supernova that created the nebula was recorded by different cultures around the world. There is evidence of its observation in Japan, China and possibly New Mexico . Strangely, there are no convincing records of it being observed in Europe. This is especially odd because another supernova that occurred 50 years earlier in AD 1006 was observed from many of the same regions, including Europe. Halley’s Comet, which appeared in AD 1066 was also recorded by Europeans.
Were Europeans not able to physically observe the supernova of 1054 for some reason or were records of it perhaps suppressed? One traditional explanation is simply that the weather was bad. However, as bright and long-lasting as the supernova was, this explanation seems implausible. Alternatively, there is circumstantial evidence suggesting that perhaps an Icelandic volcano is to blame for obscuring the sky. This hypothesis was investigated by James Ridgway and written about by Richard Stradling in 1994. Ridgway found that most famines in medieval Europe happened shortly after a volcanic eruption in Iceland, perhaps the result of dust blocking out the sun and causing crops to fail. Ridgway found evidence of famine in Germany and cattle starvation in England in 1054. Chinese records also indicate that the supernova appeared to turn red before it disappeared, which could mean that the volcanic dust had eventually reached that region.
An upheaval of the Roman Catholic Church during this period could also be responsible for the lack of documentation. On July 16, 1054, the Church of Rome formally separated from the Eastern Orthodox Church by excommunicating the Eastern patriarch and his followers in an event known as the East-West Schism. The papal legates responsible for this may have suppressed any Western writings about a visible omen – such as a new star – that could challenge their authority.
We may never know why Europeans failed to document the supernova in 1054, but the remnants of the explosion have become some of the most studied objects outside of the Solar System. The Crab Nebula and its pulsar continue to provide valuable information into the deaths of stars.
Patrick Treuthardt is assistant director of the Astronomy and Astrophysics Research Lab at the N.C. Museum of Natural Sciences.