Chinese and Arabic astronomers left historical documentation of a supernova that occurred in our own galaxy in the year 1006 (SN 1006), and another one 48 years later (SN 1054). Some of the writings about SN 1006 say there was a visual explosion half the size of the moon, and it shone so brightly that objects on the ground could be seen at night. We know these writings weren’t just fantastical imaginations because we now have the “leftovers” of these supernovae; Supernova Remnant 1006 and the Crab Nebula. But now there is more evidence. A team of Japanese scientists has found the first evidence of supernovae in an ice core sample.
The gamma rays from nearby supernova ought to have a significant impact on our atmosphere, in particular by producing an excess of nitrogen oxide. Ice cores are known to be rich in information regarding past climates, and scientists thought core samples could record astronomical phenomena, as well. In 1979, a group of researchers suggested the idea when they found nitrate ion (NO3-) concentration spikes in an ice core sample from the South Pole ice core that might correlate with the known historical supernovae Tycho (AD 1572), Kepler (AD 1604), and SN 1181 (AD 1181). Their findings, however, were not supported by subsequent examinations by other researchers using different ice cores, and the results remained controversial and confusing.
But in 2001, a team of scientists from Japan drilled a 122 meter ice core sample at the Dome Fuji station in Antarctica, an inland site in Antarctica. At a depth of about 50 metres, corresponding to the 11th century, they found three nitrogen oxide spikes, two of which were 48 years apart and easily identifiable as belonging to SN 1006 and SN 1054. The team speculates that the mysterious third spike may have been caused by another supernova, visible only from the southern hemisphere.
Additionally, the team saw a 10 year variation in the background levels of nitrogen oxide, almost certainly caused by the 11-year solar cycle, an effect that has been seen before in ice cores. This is one of the first times that a distinct 11-year solar cycle has been observed for a period before the landmark studies of sunspots by Galileo Galilei with his telescope.
They also saw a number of sulphate spikes from known volcanic eruptions such as Taupo, New Zealand, in 180 AD and El Chichon, Mexico, in 1260 AD.
The team said that by further extending their analysis to deeper and shallower ice cores would give fruitful information on galactic supernova and solar activity histories, and they are now in the process of making ionic measurements covering the past 2,000 years, including analyses of all known historical supernovae and solar periods.