Q&A: Supernova Remnants and Neutron Stars

Q:
Recent writings about supernova SN2006Gy mentioned that Eta Carinae is a potential supernova candidate in our galaxy. They mentioned that at 7500 light years it would present no harm to earth if it did explode. If a supernova exploded within say 500 light years of earth what would be the consequences of such an event? Also, if Eta Carinae did explode what magnitude would it be in the night sky, give or take a bit?

A:
Assuming that, if Eta Carinae exploded, it would be as bright as SN 2006gy, it would have a peak magnitude of about -10 (the full Moon is -12.8). That would be very bright! It could, of course, be somewhat fainter than 2006gy. The question of how close such an explosion could be before doing damage is a tricky one. At 500 light years, making the same assumption as above, Eta Car would have a peak magnitude of about -16. That's over 10 magnitudes fainter than the Sun, so there wouldn't be a significant additional source of optical flux. However, it's the higher energy radiation, such as hard X-rays and gamma rays, that would more likely be damaging to Earth's atmosphere and additional work would be needed to estimate these effects.

The worst thing might be if a beam from a close-up gamma ray burst was to strike us. But, we'd have to be really unlucky.