Scientists have recently uncovered evidence that in the year 775 the Earth was pummeled with a giant burst of radiation. The radiation left evidence behind on the earth in tree rings that formed during the year, which show high levels of radioactive compounds. The scientists say that evidence suggests the gamma ray burst was very short.
The scientists investigating the phenomenon note that our sun didn't cause the burst of radiation. Even if a strong burst of radiation occurred 1200 years ago in the form of a strong solar flare, the researchers say that there wouldn't have been enough radiation produced to leave behind the sort of evidence discovered on Earth. Scientists also say that if the radioactive burst had occurred from the sun, it would've created very bright auroras and there is no historical record of that event happening.
Astronomer Phil Plait has another suggestion for what could have caused the massive burst of radiation – a supernova. The problem with that theory, according to the astronomer, is that in order to generate the levels of carbon and beryllium discovered, the supernova would have had to been less than 1000 light years away from the Earth. He notes that such a close occurring supernova would've been so bright it would have been seen during the daylight.
There are no historical records of such a supernova occurring. Another team of scientists believes that the most likely scenario for the gamma ray burst is that it was the result of a collision between a pair of neutron stars or a neutron star and a black hole. The scientists say that such a collision would produce an extremely short gamma burst while producing no light. Researchers say that they know collisions of this sort have happened in distant galaxies in the past but such events are incredibly rare. Another member of the research team says that if the burst had been closer to the earth it could have caused significant harm to life on our planet.