The Danger of Proximity to Supernovas.
A recent study suggests that the lethal distance of a supernova depends not only on its proximity to a habitable planet but also on the level of X-rays it generates. X-rays emitted by some supernovae can strip the ozone layer from a planet like Earth, leaving it open to ultraviolet radiation from its Sun. The team looked at the X-ray spectra of nearly three dozen supernovae over the last 45 years and calculated the lethal distance for each of them. The most potentially deadly was a supernova named 2006jd, which could kill a habitable planet from up to 160 light years away.