In July of 1054, Chinese astrologers took note of the astonishing appearance of a new star in the sky. Alarmed, they quickly put a positive spin on it as there could be unpleasant consequences for not predicting such a strange event. As star-like objects appearing temporarily were referred to as ‘guest stars’, they documented the appearance of this new ‘guest star’ object as being on July 4th, giving a detailed description and noting its position in the constellation Taurus. According to their reports, so great was its brilliance, it could be seen by day for nearly a month before gradually fading. Accounts indicate it could still be seen in the night sky with the naked eye for two years before disappearing completely from sight.
What the astrologers had no way of suspecting was that the strange manifestation they documented was in fact not a new star but an old one undergoing its final death throes. Often classified today as a Type 2 nova, it involves a star roughly 8 to 15 times as massive as our sun, burning through its fuel to the point it can no longer sustain fusion reactions and undergoes a catastrophic final collapse which burns through the remaining material in a split second producing the awesome explosion such as the one witnessed a millennium ago.
Other ‘guest stars’ were observed over the following centuries but it wasn’t until modern astronomy began taking shape that sky observers began grasping what these strange objects were. In the eighteenth century, a French astronomer named Charles Messier avidly searched for comets after witnessing a spectacular comet, the great six-tailed comet of 1744. However he was greatly irked by comet-like objects or nebulae which he often at first mistook for actual comets, distracting him from his search. He began compiling a list of the various objects and their locations as a way to avoid future confusion. One of the objects he catalogued was a fuzzy diffuse object located in the constellation Taurus which he listed as M1. We know it better today as the Crab Nebula.
It wasn’t until the nineteenth century that astronomers began grasping the true nature of supernovae. In 1866 English astronomer William Huggins discovered lines of hydrogen while using spectroscopy to observe a recurring nova in T Coronae Borealis. He made the suggestion that a cataclysmic explosion might account for the unusual spectrum. Other astronomers began investigating as well but the power which lay behind these explosions didn’t become apparent until the early twentieth century when physicist Arthur Eddington speculated on the role of nuclear fusion as the source of energy for stars.
At roughly the same time, the Crab Nebula in Taurus was finally identified as the probable source of the supernova of 1054 as the Chinese had noted its location in that constellation. Along with Chinese records, historians have located a Japanese account about the ‘guest star’ as well as the writings of an Arab Nestorian christian which referenced an earlier document. Much has been made of the lack of records from Medieval Europe leading to some absurd speculation that Europeans somehow myopically failed to notice the visible by day supernova but bits and pieces of possible accounts have been located, indicating medieval scholars were not oblivious to the spectacle in the sky. The paucity of European documents is most likely the result of political turmoil in the intervening centuries leading to loss of these precious records. No doubt European astrologers would have taken note of the ‘new star’, writing and speculating about its implications for their charts, but unless there are accounts lingering in a neglected archive somewhere, it is most likely these have been lost as well.
Supernovae occur in our galaxy roughly twice in a century’s time but the last supernova visible to the naked eye occurred in 1604. The majority of time, most novae are hidden from sight by the heavy lanes of dust sprinkling the arms of the Milky Way galaxy. There’s much interest in studying them as they show the variety of ends different size stars will meet. Our sun is too low in mass to undergo a supernova explosion. Instead it will sedately burn through its fuel for about nine to ten billion years (it’s at the mid-way point right now) before swelling up into a red giant, slowly puffing off its outer layers and finally ending its days as a white dwarf star.
More massive stars (above the eight sol limit) will burn through their fuel at break neck speed, the more massive the faster. After just a few million years, they too will start to expand as super-red giants, burning first through their hydrogen, then helium, then carbon and if the star is massive enough, the core burns down to the element iron precipitating the final implosion which creates the super-nova. Because mass is so critical in determining what finally happens to the star, they are objects of intense study.
Scientists are able to observe novae happening in other galaxies but there’s nothing like a ring side view for getting an extraordinary light show. Several years ago Betelgeuse, a red super-giant nearing the end of its life began dramatically dimming, leading to excited speculation it was about to go super-nova. At roughly 600 light years distance, it would be far enough away to pose no threat to Earth but provide us the first clear view of a star exploding close up (in stellar terms). Alas, it was not to be. Betelgeuse began brightening again so all that was going on was that it was ejecting a big gob of dust and gas (the stellar equivalent of phlegm) which obscured the star for a brief time.
Still, it’s only a matter of time before a giant star in our galaxy explodes so we finally get an opportunity to witness one of the most awesome spectacles Nature can produce armed with a battery of scientific instruments available for teasing out the secrets of this stellar cataclysm.
