The world of 1054 was not a pleasant place for most people, the plague was rampant throughout parts of Europe, the Christian Church was going through a bitter split and the remains of the once great Roman Empire were contracting ever further around the Eastern Capital of Constantinople. It was in the middle of a century of change that would impact the world forever. It was in a time when astronomical goings on were recorded and feared as every plague or disaster was linked to every comet or unexplained heavenly event. When Hayley’s Comet was observed in 1066 it was attributed to the English King Harold’s downfall, though William of Normandy seemed to do quite well out of it so he probably didn’t think it was a bad omen. So when the supernova of 1054 (SN1054) was recorded it must have sent shivers down the spines of astronomers all over the Northern Hemisphere for those that saw it, what was this star that suddenly appeared so bright that it could be seen during the day, what did it mean?
They had no idea that a massive star had spent the last of its fuel and could no longer resist the force of its own gravity, that its core collapsed on itself releasing so much energy that it would briefly be brighter than the entire galaxy. They would have had no idea it would become the amazing planetary nebula known as the Crab Nebula today. Such is its significance that Charles Messier gave it the catalog title of M1.
Here’s a picture I took of M1 in about 2009.
On the 4th July 1054, the Chinese recorded the supernova that is generally agreed to be what became the Crab Nebula as it was in the right place and the timing is about right. The Chinese recorded that the light from the supernova was four times brighter than Venus and was visible during the day for 23 days. They recorded that it was visible in the night sky for 653 days and based on the descriptions it would have had a visual magnitude between -4 and -6 at its peak. A Christian physician from Baghdad, named Ibn Butlan, was resident in Cairo and Constantinople between 1052 and 1055. His observations, recorded sometime later in 1242 from his notes, linked the bright temporary star with an epidemic in 1054 – probably the plague, as this was doing the rounds in Constantinople at the time. Some rock art that depicts a star and the crescent Moon found in North America may indicate an observation of the 1054 event, as the supernova would have been visible in proximity to the Moon at various times in June and July of 1054. The observers in North America may well have seen it, though this could have easily been any other bright star in the vicinity of the Moon. Thus this link with SN1054 is not supported by academics. This image from Rockartblog shows the image, now regarded as not showing SN1054.
There is an absence of European records of the SN1054 with no specific sightings being recorded, they did record an unrelated event in 1006 in quite some detail so it is a mystery why they did not record SN1054. There is some suggestion that the events between the Catholic Church and the Eastern Orthodox Church that led to the Great Schism may have led ecclesiastical scholars to not report the supernova for fear of having it related to the schism. The absence in the European record is perplexing as if it was so visible to other parts of the Northern Hemisphere then why was it not recorded in Europe? One reason may be that the weather precluded it, it would only take a couple of months of consistently poor weather to make viewing conditions difficult rendering the supernova invisible to European observers.
Once the supernova had dimmed it got forgotten from the record, which is hardly surprising because once it was no longer visible to the naked eye no one would notice it. Of course, things were very busy indeed at the location of M1, the Crab Nebula as the collapsed remains of what was once a star had compressed into a neutron star and was rapidly spinning: a pulsar. The material ejected by the supernova explosion was moving out from the centre into what is now the distinctive shape and structure of the Nebula. The Nebula wasn’t recorded until 1731 by John Bevis from England. Bevis was an amateur astronomer and was credited at discovering a number of other objects, he was in correspondence with Charles Messier. The Crab Nebula made it into Charles Messier’s catalog in the first position as M1. Though this wasn’t because the Crab was anything spectacular to Messier. He was a comet hunter and his list was basically a list of things that were not comets, which is quite interesting because originally he mistook the Nebula for being Hayley’s Comet. The Nebula got its common name from the sketches made by William Parsons who observed the object and noted it looked a bit like a crab.
This image is from NASA, somewhat more detailed than mine, of course, was captured by the Hubble Space Telescope (HST).
A pebble dropped in a pond
At the centre of the Nebula is one of the most violent and spectacular objects in the universe, and one that I find absolutely fascinating, a pulsar. The HST has captured some amazing images, courtesy of NASA, of the effects caused by the pulsar including this series of 10 images which show waves apparently coming out of the object, these waves are travelling at half the speed of light. The pulsar is the bright star in the centre, it almost looks like a pebble dropped into a pond.
The pulsar spins at about 30 times per second and is made of ultra dense material, basically a whole pile of neutrons all packed together. So it’s the weight of what’s left over of the star all crushed down into the size of a ball of neutrons about 20km in diameter. The enormous magnetic disturbance this creates accelerates electrons around the star to nearly the speed of light.
The first time I saw M1 I was amazed to just pick out some of the structure, just fleeting as it mainly looks just like a blob of grey smudge in my telescope. But like all things I have observed the real amazement comes from understanding more about the object and how it got created and what fascinating details are hiding in its core. I find it mindboggling that everything we know about M1 has all come from observing this object from 6500 light years away.
