4 June 2012, Solar-Terrestrial Environment Laboratory of Nagoya University has been studying amounts of radioactive carbon contained in rings of a 1,900 years old cedar tree.  The tree is on Yakushima Island.

When they got to the rings which represent the year 775 AD, they discovered 20 times the normal level of radioactive carbon!

Associate Professor Kimiaki Masuda, believes the radiation came from an extraterrestrial event, such as a super nova, or massive solar flare from our own star.   The study was published by Nature.com.