In 1006, a brilliant supernova lit up Earth's skies, the brightest ever recorded. Astronomers in many parts of the world reported it. Now, a re-analysis of the writings of the Persian scholar Ibn Sina has added to our knowledge of this event.
In the 400 years since Galileo turned his telescope to the skies, no supernova has been seen within our galaxy, although we now see hundreds each year at much greater distances. There are not a lot of ways in which astronomers envy those who lived in the 11th century, but one exception is the fact that the era was punctuated by two supernovae close enough to Earth to provide spectacular shows in 1006 and 1054.
Both these events were so bright, they were visible in daylight, and each left remnants that modern telescopes now study intensively. Historical records remain valuable, however, in giving us an indication of these events' brightness.
Chinese and Japanese astronomers observed both apparitions, but records elsewhere are patchy. In Europe, the supernova of 1054 appears not to have warranted a mention, despite being four times as bright as Venus at its peak. This promoted author James Michener's much repeated quote: “An Age is called Dark, not because the light fails to shine, but because people refuse to see it.”
So the addition of an extra description of the event of 1006 is significant. On arXiv, Professor Ralph Neuhaeuser from Astrophysikalisches Institut und Universitäts-Sternwarte in Germany has provided the original Arabic from Ibn Sina's work, called Kitab al-Shifa, along with an English translation.
A Chandra space telescope image of SN 1006's remnant, taken in X-rays. NASA/CXC/Middlebury College/F.Winkler
“It remained for close to three months getting fainter and fainter until it disappeared; at the beginning it was towards a darkness and greenness, then it began to throw out sparks all the time, and then it became more and more whitish and then became fainter and disappeared,” the authors wrote in the paper.
More importantly perhaps, Neuhaeuser has refuted the previous theory that Ibn Sina was referring to a comet.
SN 1006 occurred at 42° south, making it invisible from northern latitudes, one of the factors that limited the accounts we have of the event (no such excuse applies for those who failed to report SN 1054). At the time of the explosion, Ibn Sina was living in Central Asia, far enough north that he may have struggled to witness the new star himself, and may have been relying on the reports of others.
No other record mentions the change in color from green to white that Ibn Sina refers to. While the second-hand nature of the account may make it unreliable, this color reference is something astronomers trying to explain the explosion may find useful.
SN 1006 is thought to be an example of two white dwarfs colliding, a process whose frequency is debated, but usually considered one of the rarer supernova triggers, increasing the value of any information we can collect on its evolution.