OT: Galactic sterilisation

[Baron Munchausen]

As it turns out, this argument over radiation intensity is misplaced. The full theory is that the gamma radiation from a supernova destroyed the ozone layer and allowed hard ultraviolet from our own sun to reach the surface.

http://www.cnn.com/2004/TECH/science....ap/index.html

So you were on the right track comparing to the radiation from the sun...