Expert: James Gort - 10/15/2011

Question
Dear Prof. Gort,

I recently saw an astronomy documentary about supernovas, and they said that Betelgeuse--one of the prominent stars in our night sky--is likely to go supernova anytime in the next 10,000 yrs., maybe even tonight! They quickly added that, since Betelgeuse is more than 600 light years away, the Earth is in no danger.

Who, then, WOULD be in danger? I mean, how close would be too close? And how big would the "dead zone" be after such an event (i.e., the distance out to which any and all lifeforms would face certain death)?

Thanks,
Everette

Answer
Hello Everette,

You've asked a very interesting question, and one in which there has been some research, but no definitive answer. But I'll give you the best current guess.

First, some history. You've probably heard of the Crab Nebula, which formed when a star 6500 light years away went supernova in the year 1054. At its brightest, it appeared to be -7 magnitude (a guess), but certainly visible in the day time. How close would that star need to be, to appear as bright as the sun (about -26 magnitude)? A quick calculation tells me it would need to be about 1 light year away (closer than any other star). But at that distance, even though its visual brightness would be the same as the sun's, its gamma rays, x-rays, and neutrinos would far exceed the sun's and I'm sure it would be lethal.

So what is the dead zone? Based on more detailed calculations many people have made, a Type II supernova (like Betelgeuse would become) needs to be closer than about 30 light years for major damage (widespread death) on earth. A Type Ia (formed by a double star, and it's more powerful) would need to be closer than about 80 light years for the same damage.

BTW, since Betelgeuse is 10 times closer than the Crab, it would be quite spectacular, even in the day time.

Hope that helps.

Prof. James Gort